But what makes a good power supply, anyway? Most assume that power supplies carrying higher wattage ratings are superior, but as the collapse of the so-called “megahertz myth” illustrates, higher numbers aren’t always better. First and foremost, a power supply should deliver clean, consistent power to system components. Power supply efficiency is also important; an efficient power supply can save you money on every electricity bill, especially if you have your system running 24/7. Environmental variables like temperatures and noise levels matter, too.
Armed with a couple of test systems, temperature probes, noise level and power consumption meters, an oscilloscope, and an all-important bathroom scale, we can test all those metrics, plus a few others, ourselves. There’s no need to rely on manufacturer spec sheets, marketing claims, or wattage ratings. Are cheap, generic power supplies really that much worse than high-end models that cost twice as much, or more? And among those high-end power supplies, is there really much difference from manufacturer to manufacturer? Let’s find out.
Here’s how the power supply units (PSUs) we’ll be looking at compare in terms of specifications. By the way, the SH-ATX465P4 is a no-name unit I picked up at a local shop for $40 for the sake of comparison.
|Antec NeoPower||480W||Active||1 120mm||3 years||$110|
|Enermax EG485P-SFMA24P||485W||Passive||2 80mm, 1 blower||3 years||$129|
|OCZ PowerStream||520W||Passive||2 80mm||5 years||$130|
|SH SH-ATX465P4||465W||NA||2 80mm||NA||$40|
|Silverstone SST-ST30NF||300W||Active||None||3 years||$155|
|Ultra X-Connect||500W||None||2 80mm||1 year||$99|
|Vantec Ion 2||350W||None||1 120mm||3 years||$45|
|Zalman ZM400B-APS||400W||Active||1 80mm||1 year||$87|
I should mention that we also invited RaidMax, Thermaltake, and PC Power & Cooling to participate in this comparison, but they either declined or didn’t respond to our requests.
We’re looking at a full range of power supply wattagesfrom 300W all the way up to 520W. Conventional wisdom would probably suggest that more wattage is better, but as we’ll soon see, the PSUs with lower wattage ratings hold their own.
In addition to a range of wattages, we also have several power factor correction (PFC) implementations. Power factor (PF) is the ratio of true power to apparent power where true power refers to power that’s actually being consumed and apparent power is calculated by multiplying the voltage by the current being drawn. If voltage and current are out-of-phase, apparent power will be greater than real power. This is a common condition for circuits that contain capacitors and inductorspower supplies being a perfect exampleand it results in a PF less than 1. PFC aims to bring voltage and current back into phase, raising the PF towards a goal of 1, where real power equals apparent power.
In their quest for a more ideal power factor, the Antec, Silverstone, and Zalman power supplies employ dedicated circuitry to correct out of phase voltage and current. This is referred to as active PFC. The Enermax, and OCZ power supplies use passive components like capacitive filters to correct power factor, which is appropriately referred to as passive PFC. In general, active PFC results in a higher power factor than passive PFC, which in turn results in a higher power factor than no PFC at all. But does having a higher power factor really do you any good?
Yes and no.
If you’re a large business running banks of machines, the power company may charge you for the apparent power draw you present to the grid rather than your real power consumption. In this case, a lower power factor can cost you money over time. If you’re running an uninterruptible power supply (UPS), a lower power factor can also result in shorter run times off battery. However, if you’re a regular home user with no UPS and no power factor-related charges on your electricity bill, PFC isn’t going to do anything for you. It will, however, make your local power company happy; higher client power factors allow for more efficient distribution of power across the grid.
Speaking of efficiency, overall power supply efficiency is also something to consider. In this case, efficiency refers to the percentage of real power drawn by the power supply that’s actually delivered to system components. More efficient power supplies will draw less real power to run a system, saving even home users on electricity costs. More efficient power supplies should also run cooler since the percentage of real power drawn that isn’t delivered to system components is radiated as heat. Not all power supply manufacturers publish efficiency specs, but we’ll be able to compare the relative efficiency of the power supplies we’re looking at by measuring real power consumption at the outlet.
Our stack of power supplies offers plenty of variety on other fronts, like cooling. At one end of the spectrum, there’s a passively cooled unit from Silverstone. At the other, we have an Enermax unit with two fans and a blower. And, of course, there are a number of single and dual-fan implementations in between. We’ll see how different cooling designs impact system temperatures and noise levels in a moment.
On the warranty front, three years seems to be the consensus. There are a few deviations, though. OCZ deserves extra praise for offering a generous five-year warranty, while Ultra and Zalman should be scolded for their stingy one-year warranties. Since a quality power supply can potentially handle a few years worth of system upgrades, a good warranty is essential.
Finally, we come to price, where we have quite a spread. There’s a $115 gap between our cheapest and most expensive PSUs and plenty of models to fill in the gap. It’s interesting to note that our two lowest wattage PSUs are so far apart in price. Vantec’s 350W Ion 2 retails for only $45, while Silverstone’s passive 300W PSU sells for more than three times that.
Wait, there’s more. Each of the PSUs we’re looking at also has a different mix of power connectors. Rather than go through them all individually, I’ve listed them in a handy chart below.
|PSU||Main power||8-pin EPS||6-pin PCI-E||6-pin AUX||4-pin P4||4-pin peripheral||SATA||4-pin floppy|
|Antec NeoPower||24-pin||0||1||0||1||6, 2||2, 2||0*|
|OCZ PowerStream||24-pin||1||0||1||1||6, 2||2||2|
|Vantec Ion 2||20-pin||0||0||1||1||6||2||2|
*The NeoPower comes with a splitter that yields two four-pin floppy connectors, but it will use up one of the PSU’s four-pin peripheral connectors
**Ultra X-Connect owners are entitled to a free SATA splitter that serves up two SATA power connectors at the expense of one Molex peripheral connector Note that the OCZ PowerStream is the only power supply of the lot with an eight-pin EPS power connector for high-end server and workstation boards. The Antec and Enermax PSUs are the only ones with six-pin PCI Express power connectors. The Antec, Enermax, and OCZ power supplies are also the only ones with 24-pin main power connectors. 24-pin power connectors are common on dual-processor motherboards and many new LGA775 boards, but for more common 20-pin boards, the 24-pin power supplies ship with 24-to-20-pin adapters.
I’ll explain why the Antec and OCZ PSUs have two different connector counts listed for some of their power connectors when I discuss those power supplies individually.
Although a power supply’s total wattage can be helpful, it’s more interesting to look at how current and wattage is spread across each voltage rail. I’ve summarized current and power maximums for each power supply below.
Unfortunately, manufacturers don’t necessarily provide max current and power ratings for the same AC input voltage. Antec, Enermax, OCZ, and Zalman’s numbers correspond to the full range of AC input, but Vantec only provides numbers for 115V AC, and Ultra only for 230V AC input. Silverstone provides numbers for both, and there’s no telling what our generic SH power supply’s maximums correspond to.
Maximum output current (A)
|Antec NeoPower||30||38||18, 15|
|Enermax EG485P-SFMA24P||34||40||16, 15|
|Silverstone SST-ST30NF (100-120V)||21||20||17|
|Silverstone SST-ST30NF (200-240V)||25||23||18|
|Ultra X-Connect (230V)||28||30||34|
|Vantec Ion 2 (115V)||14||30||15|
With some of the PSUs listing max output current for different input voltages, it’s hard to compare numbers across the board. There are a few things worth noting, though. First, both the Antec and Enermax PSUs sport dual 12V rails. Antec’s dual 12V rails combine for a max output current of 32Aone amp lower than the sum of their individual max currents.
Also note that current across the Silverstone PSU’s +5 and +12V rails is capped between 30 and 35A, depending on the input voltage. Components won’t be able to draw maximum current from both rails at the same time. Overall, the Silverstone’s +5V max currents are also pretty low. Notice, also, the relatively low +3.3V max current on the Vantec Ion 2. That PSU’s 12V rail tops out at a low 15A, too. The Zalman PSU’s +12V rail looks a little weak, as well, in comparison with its relatively strong +3.3 and +5V rails.
Finally, check out the monster +3.3V and +5V rails on our generic SH PSU. Perhaps they should have diverted some of that current to the +12V line, which looks weak by comparison.
With a little help from Ohm’s law, it’s easy to translate maximum currents to maximum output power. However, there are some additional limits on what the PSUs can handle with combined +3.3V and +5V loads. Let’s look at those limits.
Maximum output power (W)
|Antec NeoPower||100||190||216, 180|
|Enermax EG485P-SFMA24P||113||200||192, 180|
|Silverstone SST-ST30NF (100-120V)||70||100||204|
|Silverstone SST-ST30NF (200-240V)||83||115||216|
|Ultra X-Connect (230V)||93||150||408|
|Vantec Ion 2 (115V)||47||150||180|
The table above may be a little confusing, so allow to me illustrate how to read it with an example. All the numbers you see are max wattages, and some of the cells in the table extend across multiple columns because of shared maximum capacities. The Enermax unit can supply a maximum of 113W on the +3.3V rail and 200W on the +5V rail, as the table shows. However, the two rails cannot together exceed 280W of total output. The Enermax also has two +12V rails, one of which can output 192W while the other peaks at 180W. Combined, the four rails of the Enermax PSU can supply a maximum total of 480W. The bottom, shared cell for the Enermax that extends across all three columns delineates this total shared max capacity.
Clear as mud?
You should be able to read the specs for the other PSUs using the same basic methods. Shared cells mean shared max capacities, and not every PSU is arranged the same, so not every entry in the table is organized the same. Note that the Antec and OCZ PSUs are distinguished by their lack of shared capacity between the +3.3V and +12V rails; both can max out their +3.3V and +5V rails simultaneously.
Antec gets modular Antec power supplies have won awards and accolades in both of our previous PSU round-ups, so our expectations were high for the company’s new NeoPower 480W. The NeoPower is a somewhat radical design in that its peripheral power connectors are detachable. One may connect and disconnect them from the PSU as needed. This modular design makes for much cleaner system internals than usual, provided that not all the power leads are occupied. Gone are the days when a bundle of unused power connectors must be zip-tied together and tucked away into a corner of the case.
Although its lack of peripheral power leads will draw stares, the NeoPower isn’t much to look at otherwise. The PSU’s flat titanium-grey finish is, well, dull. The muted aesthetic may blend well with aluminum cases, though.
Rather than use multiple fans to keep the NeoPower cool, Antec relies on one internal 120mm fan. The fan is temperature controlled and there’s plenty of venting at the rear, so it should do a reasonably good job of keeping things cool without making too much noise. The NeoPower also has a couple of “fan only” four-pin Molex connectors that can control system fan speeds in step with the power supply fan.
The NeoPower’s peripheral cables all come separately, which is really quite snazzy. There’s nothing particularly special about the cables themselves, though.
What is special is what you can do with to the cables. Antec bundles the NeoPower with extra four-pin Molex and SATA connectorstwo of eachthat can be clipped onto available power leadsright on to the wires. The extra connectors are a great idea, especially since their judicious use can result in extra-tidy cable routing.
Say that three times fast The Coolergiant/Enermax EG485P-SFMA24P is easily the most awkwardly named power supply in this comparison. The unit comes from Enermax and Coolergiant, but apparently neither company could come up with a better name. For the sake of brevity, I’ll be referring to this PSU as an Enermax unit for this comparison.
In addition to having the lengthiest name, the Enermax power supply is also longer than most of the PSUs in this comparison by about an inch. The extra length makes squeezing Enermax unit into smaller mid-tower cases a bit difficult, but once you shoehorn it into place, the extra inch isn’t a big deal.
With more gold than a rapper’s smile, the Enermax PSU’s bling value is off the charts. Between the brushed gold casing and polished fan grills, the bling-bling might be a little excessive, but there’s no accounting for taste.
Gold finish aside, the Enermax unit is dialed when it comes to cooling. The PSU is equipped with two 80mm cooling fans and a neat little blower that pulls air from the case. Fan speeds are controlled by an analog knob at the back of the unit, making the Enermax easy to fine-tune for more cooling or lower noise levels.
The Enermax PSU has a massive array of cables that not only includes a six-pin PCI-E connector, but also four SATA plugs out of the box.
If those four SATA connectors aren’t enough, Enermax also throws in a SATA splitter to power an additional two devices. The PSU also comes with a 24-to-20-pin power adapter for motherboards with 20-pin plugs.
Redemption? The PowerStream is OCZ’s first foray into the power supply business, and the company isn’t being shy about offering a high-end unit right off the bat. Everything about the PowerStream screams enthusiast, which is exactly what I like to see.
For better or worse, the PowerStream has the distinction of being the largest power supply in this comparison. It’s about half an inch longer than the Enermax unit and a major pain to squeeze into smaller mid-tower cases. Some of the pain comes from trying to squeeze the PSU into the case, but even more comes from the fact that it’s impossible not to scratch the PSU’s gorgeous mirror finish in the process.
The PowerStream’s mirrored pewter finish manages to be sexy without being gaudy. There’s some green internal lighting that comes on when the PSU is powered up and even a little bling with polished gold fan grills, but nothing too garish.
The gold fan grills cover a couple of 80mm fans that channel air across the top of the case. Neither fan faces the system’s processor, which could result in higher CPU temperatures. We’ll test that in a moment.
Borrowing an idea from Antec’s TrueControl power supply, the OCZ PowerStream lets users adjust the voltage of each of the rails. Voltages options range from 2.8 to 3.8V, 4.5 to 5.5V, and 10.8 to 13.2V for the +3.3V, +5V, and +12V rails, respectively. When you’re within 5% of a rail’s intended voltage, an indicator light will change from orange to green. If 5% isn’t close enough for you, it’s easy to drop into the system’s BIOS or use Motherboard Monitor to fine-tune voltage further. A word of caution, though: Motherboard Monitor and motherboard BIOSes don’t always display voltages correctly.
The PowerStream is loaded with cables, each of which is either neatly sheathed or twisted to avoid tangles and clutter. Notice that two of the PSU’s four-pin Molex connectors are sheathed in a special casing. According to OCZ, this is to provide cleaner power to sensitive hard drives and graphics cards.
A 24-to-20-pin power adapter and bundle of zip ties round out the PowerStream package. The zip ties are a particularly nice touch, since I’ve never set up a system without using at least a couple to tidy up power supply cables.
Before I wrap things up on the OCZ PSU, it’s worth reiterating the fact that the PowerStream carries a five-year warrantytwo years more than any other PSU in this comparison. When you’re dropping $130 on a power supply, extra coverage makes it much easier to justify the expense as an investment.
Generic, baby We’ve had several requests to include a generic power supply in our comparisons, so this time around, I picked up an SH brand 465W unit from a local shop. For the equivalent of $40, 465W of “P4 approved” power seems like a deal. I could have opted for an even cheaper power supply with a lower wattage rating, but we’ll be testing with some pretty high-end hardware, and I didn’t want to risk frying anything.
Unfortunately, information on the SH-ATX465P4 is scarce; the PSU doesn’t even come in a box. Here are a couple of photos for reference, though. I’d say more, but there’s really nothing special about this PSU that a couple of captioned pictures can’t illustrate.
0dB How is it that the most expensive power supply in this comparison also offers the lowest wattage? Silence. No, I’m not talking about special low-noise fans. I’m talking about absolute silence that can only be delivered by passive cooling. Silverstone’s SST-ST30NF is the first passively cooled PSU to grace the Benchmarking Sweatshop, and given the recent trend towards silent computing, I’m betting that it won’t be the last.
With lots of internal venting, cooling ridges, and fins, the Silverstone unit is definitely dialed for passive cooling. To be honest, though, I was expecting taller fins with more surface area. The PSU will certainly heat up under load, but with so many cooling fins radiating heat inside the case, more aggressive system or processor cooling may be needed to compensate.
How hot does the Silverstone unit get? Hot enough to cause extreme discomfort if you touch it for only a second. When the PSU is running at full tilt, you could probably cook an egg on it and maybe a side of sausage or bacon. Thankfully, Silverstone equips the PSU with a handy temperature warning light that warns you when it’s too hot to handle.
Silverstone doesn’t offer anything special in the cabling department, which is disappointing for a $155 power supply. Motherboard power connectors are sheathed, but that’s about it. The leads are also a little on the short side, which could create problems in mammoth full tower cases.
I should mention that Silverstone claims the power supply’s 300W rating is very conservative. The PSU apparently packs a deep reserve that offers over 400W of peak power. We’ll be putting that assertion to the test shortly.
Modder’s delight Although I can only ever remember seeing Ultra-branded products in the Tiger Direct catalog, the company is branching out, and its new X-Connect line of modular PSUs is available from a number of different retailers. A friend of mine raves about his X-Connect 500W, and after seeing the PSU, I just had to include it in this comparison.
What can I say? I’m a sucker for gorgeous modular PSUs. Like the Antec NeoPower, the Ultra X-Connect’s power cables can be detached from the PSU as needed. Ultra takes things one step further than Antec by making the motherboard power connectors removable, as well.
If you’re into bright, shiny things, the X-Connect will definitely catch your eye. The PSU has a mirrored blue finish that’s looks gorgeous against the PSU’s silver fan grills and accents.
Speaking of fans, the X-Connect’s cooling setup is pretty standard: one 80mm fan above the system processor and another at the rear. I’m a little worried that fancy grill on the internal fan will restrict airflow, though.
The X-Connect’s big claim to fame is its modular cables, which are all neatly sheathed in a UV-reactive casing that glows under black light. Groovy. If you have a case window and UV cold cathode, this PSU will definitely add some visual flair to your system. Ultra even wraps its own casing around the power plugs to give the cables a more polished look. Unfortunately, that casing makes the plugs a little thicker than normal. The slightly thicker plug casing shouldn’t be a problem in most systems, but I had to hack it away to get the power connectors to fit on the admittedly tight Abit KV8-MAX3 motherboard.
Gorgeous looks and swanky cables aside, the Ultra X-Connect isn’t all roses. The PSU’s one-year warranty is disappointing, especially given the $99 list price and the fact that virtually very other PSU in this comparison carries at least a three-year warranty.
Update 11/11/2004 – Ultra now offers a three year warranty extension for its X-Connect power supplies.
How much? The Vantec Ion 2 power supply is only $5 more expensive than the generic SH unit I picked up for testing. The Ion 2 is also the lightest PSU in the comparison, and it’s only packing 350W of power. That doesn’t give me a lot of faith in the Ion 2’s capabilities going into this comparison, but I’ve always liked underdogs. At the very least, the Ion 2 has the potential to be a surprising low-cost contender.
At least the Ion 2 doesn’t look like a cheap, generic PSU. It actually looks a lot like the Antec NeoPower, minus the dull grey finish and modular cables.
The Ion 2 uses a massive 120mm fan and plenty of venting at the rear to keep things cool. The fan is temperature-controlled, but unlike the Antec unit, the Ion 2 doesn’t offer any “fan only” power connectors for temp-controlled system fans.
Vantec scores big points for the Ion 2’s cables, though. Every cable is sheathed, from the motherboard connectors to all the floppy plugs. On a $45 PSU, that’s incredible. Like the Silverstone PSU, power leads are a little too short for use in monster full tower cases, but there’s plenty of length for mid-towers.
As if sheathing every cable weren’t enough, the Ion 2’s four-pin Molex connectors also come with “EZ-Grip” plugs. As the name implies, the plugs are easier to handle than standard four-pin connectors. Unplugging devices is effortless, which is admittedly a minor issue, but it’s one more little thing that Vantec has done right with the Ion 2.
While EZ-Grip is handy, it’s not perfect. The thicker power plugs don’t sit flush on graphics cards like the Radeon 9800 XT, but trimming the offending clip takes all of a couple of seconds with a pair of scissors.
Active PFC under the hood Although Zalman was displaying a passively cooled external 400W PSU at Computex not long ago, that PSU isn’t ready for prime time yet. Zalman does have a new internal model, though. The ZM400B-APS packs active power factor correction and 400 watts of power, so it could be a dark horse in this comparison.
And I meant dark horse literally. The Zalman PSU comes dressed in black, which could become the new beige for PC cases and components.
The flat black finish is decidedly conservative, and so is the power supply’s cooling. Zalman relies on a single 80mm exhaust fan to keep the PSU cool, although there’s some extra venting on the inside to help draw warm air out of the system. Still, the single 80mm fan has me wary of the PSU’s ability to keep a system cool while maintaining low noise levels.
The Zalman’s cabling is a simple affair. After seeing every cable sheathed on the Vantec Ion 2, which costs half as much as the Zalman unit, it’s disappointing that none of the Zalman’s power cables are sheathed in any way.
There’s a little redemption lurking for Zalman inside the box, though. The PSU comes with a fan splitter that adapts a four-pin Molex connector to power three-pin fans. Zalman also includes four Velcro cable ties, which are a little classier than zip ties.
Unfortunately, redemption is short-lived. Zalman’s one-year warranty for the PSU is really not enough, especially considering the $87 price tag and the fact that just about everyone else in this comparison offers three years of warranty coverage or more.
All tests were run three times, and their results were averaged, using the following test systems.
|System||Athlon 64||Dual Opteron|
|Processor||AMD Athlon 64 3200+ 2.0GHz||AMD Opteron 246 2.0GHz (2 processors)|
|Front-side bus||HT 16-bit/800MHz downstream
HT 16-bit/800MHz upstream
|Motherboard||Abit KV8-MAX3||Tyan Tiger K8W|
|North bridge||VIA K8T800||AMD-8151 AGP tunnel|
|South bridge||VIA VT8237||AMD-8111 I/O hub|
|Chipset drivers||Hyperion 4.53||AMD chipset driver pack 2.10|
|Memory size||512MB (1 DIMM)||2GB (4 DIMMs)|
|Memory type||Corsair XMS3500 PC3000 DDR SDRAM||Corsair CM72SD512RLP-3200/S Registered PC3200 DDR SDRAM|
|Graphics||ATI Radeon 9800 XT||NVIDIA GeForce 6800 Ultra|
|Graphics driver||Catalyst 4.9||ForceWare 61.76|
Liteon 16X DVD-ROM
Hitachi Deskstar 7K250 SATA 250GB
Maxtor 740X-6L ATA/133 40GB
|Operating System||Windows XP Professional SP2 with DirectX 9.0c|
I put together a couple of test systems for this comparison. The first is a moderately taxing Athlon 64 3200+ with a Radeon 9800 XT and few other accessories. The second is a monster of a dual Opteron workstation with a GeForce 6800 Ultra, 2GB of RAM, and a stack of 10K-RPM hard drives. The DC voltage and AC ripple of each PSU was tested at idle and under load for both tests systems. I also used the Athlon 64 system for our temperature and noise level tests inside an Antec Lanboy enclosure with a Vantec Stealth 80mm exhaust fan.
Systems were tested at idle and under a load consisting of Folding@Home, HD Tach’s read transfer test, and a looping 3DMark03 Mother Nature demo at 1600×1200 with antialiasing and anisotropic filtering cranked all the way up. I used the following versions of each application:
The test systems’ Windows desktop was set at 1280×1024 in 32-bit color at an 85Hz screen refresh rate. Vertical refresh sync (vsync) was disabled for all tests.
All the tests and methods we employed are publicly available and reproducible. If you have questions about our methods, hit our forums to talk with us about them.
There’s a general consensus that the heavier a power supply is, the better it is. I’m not sure if there’s a proper rationale for that consensus. Perhaps the assumption is that heaver PSUs have more goodness inside. More likely, it’s the fact that we generally perceive heavier objects to be more sturdy and reliable.
To kick things off, I dragged the PSUs into the bathroom to weigh them on the scale. This is a pretty generic bathroom scale, and although it has a fancy digital display complete with one digit after the decimal point, I still had to weigh the PSUs while standing on the scale to get a reading at all. After subtracting my weight, I was able to approximate the weight of each PSU.
The Ultra and Silverstone PSUs are the heaviest of the lot, but I’m not sure it’s because of more goodness inside for either. The Ultra’s fancy cable sheathing appears to add some weight, and the Silverstone PSU’s reliance on passive cooling could account for some of its heft. At the other end of the spectrum, the Vantec Ion 2 wins the featherweight crown. It’s lighter than our generic SH PSU and a little more than half the weight of our heaviest PSUs. Of course, we won’t know if this weight theory pans out until we look at some other performance metrics.
I used Motherboard Monitor to measure the CPU and system temperatures of our Athlon 64 test rig in an Antec Lanboy case. To best simulate a real-world system, I added a Vantec Stealth 80mm exhaust fan and an aftermarket Thermaltake Silent Boost K8 processor cooler. Since many enthusiast-oriented motherboards are sporting temperature-controlled processor and system fans these days, I let the KV8-MAX3 manipulate system and processor fan speeds based on system temperatures. Fan speed temperature thresholds were consistent for each PSU. Ambient room temperature was maintained between 26.5 and 27 Celsius.
Measurements were taken after 10 minutes idling at the Windows desktop and after a further 10 minutes under our Folding@Home/HD Tach/3DMark03 load. The system was allowed to cool for 20 minutes with the case panels off between each PSU test.
At idle, there isn’t much variation in temperature between the power supplies. The Enermax PSU’s high fan speed setting manages a slightly lower processor temperature, but only by a degree. The Silverstone and SH PSUs, on the other hand, produce higher system temperatures by a degree.
Under load, the most we can manage is a two-degree spread in CPU temperatures and a three-degree spread for system temps. As expected, the Silverstone PSU leads the way with the highest temperatures on both fronts. Zalman and Ultra’s cooling solutions don’t look so great, either.
At the other end of the spectrum, the Antec and Vantec PSUs produce the lowest CPU and system temperatures of the lot. Considering that both use a single 120mm internal fan and ample venting at the rear, it’s not surprising that they perform similarly in this test.
Noise levels were measured 1″ from the front and rear of the test system using an Extech 407727 digital sound level meter. The meter was placed out of the direct path of airflow.
The Antec, Enermax, and Silverstone PSUs round out our quietest top three at idle. Given its passive cooling, it’s a little surprising that the Silverstone PSU doesn’t result in lower noise levels. I suspect that the system’s temperature-controlled fans have to work harder and louder to compensate for the extra heat radiating from the PSU.
Our generic SH power supply shows its first sign of real weakness in our noise level tests, at least at idle. What happens under load?
The SH power supply makes our system even louder. Silverstone’s passive PSU loses some luster here, too, as system and processor fans spin faster to expel heat radiating into the case from the power supply’s cooling fins.
The Antec, Enermax, and OCZ units are among the quietest PSUs under load. Interestingly, the Enermax PSU is quietest with its high fan speed setting, perhaps because its blower can more quietly vent warm air from the case than our temperature-controlled system fan. The Ultra and Zalman PSUs also contend for the lowest noise levels under load, but they’re either too loud from the front or the rear to consistently stay in the top three.
I used my trusty watt meter to measure power consumption at idle and under the same load as our temperature and noise level tests. The watt meter measures the power consumption of the entire system, sans monitor, at the outlet.
On the efficiency front, Silverstone, Enermax, and Vantec round out the top three at idle and under load while the Antec NeoPower sucks power like it’s going out of style. Well, maybe it’s not that bad, but at idle the Antec PSU does pull 10W more than the nearest competitor and a little under 30W less than the frugal Silverstone unit.
With our more demanding dual Opteron system, the Silverstone PSU continues to pull fewer watts than the competition. Enermax’s PSU also continues to score well in our power consumption tests.
Voltage tests were conducted over a 100 second time interval with a Pico ADC-212/3 digital oscilloscope. There was very little voltage deviation over the time interval, so the results are averages.
There’s quite a bit of range in idle voltage across the power supplies, but everyone’s within a few percent of their respective rails. There are a couple of interesting things to note, though. First, the SH power supply has the strongest 3.3V rail. That jibes with the PSU’s spec sheet, which boasts the strongest maximum 3.3V current of the bunch.
It’s also interesting to see the OCZ power supply’s rails off the mark at all. I took the time to dial them in using the motherboard’s BIOS, but apparently the BIOS readings were wrong. I’m more inclined to believe our swanky digital oscilloscope than a motherboard BIOS that gets updated on an almost monthly basis, but in any case, the OCZ’s voltages are well within acceptable tolerances.
Perhaps the biggest surprise is the Antec PSU’s low 12V rail, especially since it has two independent 12V lines. We’ll be keeping an eye on that as the tests unfold.
Under load, the overall picture doesn’t change much at all. The power supplies stack up much like they did at idle.
Our dual Opteron system is quite a bit more demanding than our Athlon 64 test bed, but you wouldn’t know it looking at idle voltages. Not even the relatively low-wattage Silverstone PSU bats an eyelash. The 350W Vantec’s 3.3V rail’s a little lower than I’d like to see, but it’s within Vantec’s 5% tolerance.
With everyone else within 3% of target voltages on a loaded dual Opteron system, I’m pretty impressed. Still, Antec’s in-spec but comparatively low 12V rail irks me.
Again, not much changes under load. I was half expecting one of the lesser PSUs to burst into flames once I had the dual Opteron system humming at full tilt, but it didn’t happen. Even our generic SH power supply stays within tolerances, though its 12V line drops a little.
AC ripple, the AC component of what should otherwise be DC power, was measured over the same 100 second interval as our DC voltage tests. Since there’s all sorts of variance, I’m busting out some line graphs so show ripple at idle and under load across the entire time interval. The less AC ripple on each DC rail, the better.
Unfortunately, with eight PSUs, it’s impossible to graph them all together on a readable graph. I’ve graphed each PSU separately, combining idle and load ripple voltage on the same graph to make things a little denser.
There isn’t much ripple on any of the 3.3V rails, at least not on our Athlon 64 test system. The Zalman unit appears to have less ripple than any of the others, though.
Not much changes moving to the 5V rail. We’re still not seeing a whole lot on the ripple front, and that’s a good thing.
And this, ladies and gentlemen, is why I don’t recommend generic power supplies. Compared to the rest of the field, whose 12V DC rails have hardly any AC ripple, the SH power supply is all over the map under load. AC voltages are still within plus or minus 0.2 volts, but they’re much higher than the competition.
Moving to our dual Opteron system…
Not even our dual Opteron system can coax excessive AC ripple from our power supplies on the 3.3V rail. Silverstone and Zalman look particularly tight here.
Not much changes moving to the 5V rail, where everyone’s pretty close. Silverstone and Zalman continue to exhibit a slight edge, though.
This is why generic PSUs don’t belong in high-end systems. The SH power supply’s 12V AC ripple is a mess under load, much worse than anyone else’s. I’m a little concerned about the Vantec and Zalman PSUs, too. They’re not exhibiting nearly as much ripple as the SH PSU, but there’s a definite jump in AC ripple from idle to load.
I have to admit that I’m a little shocked that our passively cooled, 300W Silverstone PSU is showing the least 12V ripple under load. It’s not by much, but Silverstone has been consistently ahead of the rest of the pack, whose ripple profiles share roughly the same amplitude.
It’s not easy to come to come up with sweeping conclusions about the power supplies we’ve seen today. I’m not convinced that adage that heavier power supplies are better holds water anymore, though. Here’s a quick summary of my thoughts on each unit: Antec NeoPower The NeoPower’s modular design is a huge improvement over the mess of unused cables that plagues most systems, and I suspect we’ll see all high-end power supplies eventually jump on the bandwagon. Antec also scores points for the NeoPower’s remarkably low noise levels, consistent voltages, and low AC ripple. Unfortunately, our NeoPower suffers from a low 12V rail and high power consumption. Neither are deal breakers, especially since our 12V readings are within Antec’s +/- 3% tolerances, but they hold the NeoPower just shy of Editor’s Choice gold.
Coolergiant/Enermax EG485P-SFMA24P Despite its garish looks and awkward name, I’m quite impressed with the EG485P-SFMA24P. This power supply’s voltages are consistent, ripple is low, and efficiency is quite good. The Enermax’s noise levels and cooling potential are easily adjusted, too. Quality doesn’t come cheap, or in this case pretty, but Enermax unit earns a shared Editor’s Choice Gold award nonetheless.
OCZ PowerStream I loved adjustable voltage rails when Antec put them on its TrueControl power supply, so it’s no surprise that I love them on the PowerStream. The PowerStream combines that with a classy mirror finish; an array of cables that are either shield, sheathed, or neatly wound; and great performance in our voltage tests. Throw in a five-year warranty and eight-pin EPS support for server and workstations boards, and we have our other Editor’s Choice Gold recipient.
SH SH-ATX465P4 Although the SH power supply we picked up for testing probably isn’t the worst generic brand out there, its shortcomings are immediately apparent when one looks at AC ripple on the 12V rail. Even on our relatively conservative Athlon 64 system, the generic unit had trouble keeping up with the competitioncompetition that includes several power supplies with lower wattage ratings. Your system deserves better.
Silverstone SST-ST30NF If there were an award for cojones, Silverstone would get it hands down. Don’t let this power supply’s 300W rating deceive you. It had no problem handling our dual Opteron system under a punishing load, although I’m not sure I’d want to rely on the power supply’s deep reserve on a day-to-day basis. Overall, the Silverstone PSU boasts some of the most impressive AC ripple and power consumption scores of the lot. Not bad for passive cooling. Unfortunately, passive cooling doesn’t come cheap. $155 is a lot to drop on something that says 300W, but if you’re on a quest for the quietest system on the block, the Silverstone’s SST-ST30NF is the place to start. Editor’s Choice Silver for Silverstone.
Ultra X-Connect If aesthetics are your main concern, Ultra’s X-Connect is the swankiest power supply of the group. With a mirror blue finish and gorgeous UV-reactive modular cables, the X-Connect is a case window’s dream. Performance is pretty decent, toonothing spectacular, but no major problems either. Unfortunately, the X-Connect’s chances at stardom are ultimately stymied by the power supply’s relatively high noise levels and stingy one-year warranty.
Vantec Ion 2 Although the Ion 2 doesn’t have the horsepower to handle systems like our dual Opteron monster, this lightweight power supply is a heck of a deal at $45. With cable sheathing throughout, low noise levels and power consumption, and consistent performance on our Athlon 64 system, it’s easy to recommend the Ion 2 for less demanding systems with limited budgets. Incredible value gets the Ion 2 an Editor’s Choice Silver.
Zalman ZM400B-APS Although the Zalman’s performance is pretty decent across our exhaustive battery of tests, AC ripple on the 12V rail was a little flaky with our dual Opteron system under load. That has me worried about this 400W power supply’s ability to handle monster systems. More importantly, I’m unimpressed with the power supply’s one-year warranty. Zalman can surely do better for an $87 power supply, especially when Vantec supports its $45 Ion 2 for three years.
In the end, there’s a clear difference between generic power supplies and name brand units from major manufacturers. There’s also quite a bit of variation from one name brand power supply to another, so long as you know where to look and what’s important.