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Four killer PSUs go head to head

Geoff Gasior
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I’ve tried to pen the introduction for this latest power supply round-up at least half a dozen times now. Each time I sit down to write, I draw a blank. The stack of PSUs to my left provides little inspiration, and although our beastly load generator remains one of the most impressive pieces of hardware in my lab, the sight of its chunky switches, imposing banks of resistors, and massive fans has failed to get my creative juices flowing. I’ve even tried imbibing various intoxicants, to no avail. Such is the tortured life of a hardware reviewer.

The problem, I think, is the subject matter at hand. PSUs just aren’t that exciting, especially when compared to CPUs, graphics processors, chipsets, motherboards, hard drives, notebooks, netbooks, sound cards, enclosures, coolers, and just about everything else we cover here at TR. Don’t hit the back button on your browser just yet, though, because what PSUs lack in excitement they more than make up in importance.

A power supply may look like little more than a glorified AC-to-DC converter, but the flow of electrons it generates is the lifeblood of a modern PC. If that stream of current is dirtied, either by too much AC content or sagging DC voltages, system stability and even overclocking potential can suffer. Substandard PSUs can fail in epic fashion, too, sometimes taking other components with them in a puff of very expensive smoke. I guess that qualifies as excitement, just not the sort you’d actually want.

As in many markets, the new hotness comes to PSUs at the high end before trickling down to lower-wattage units. Today, we’ve gathered four new enthusiast-oriented models from Corsair, Enermax, Seasonic, and XFX to see how they fare against our beastly load generator. With wattages between 750 and 850W, these PSUs easily have enough power to fuel a high-end system. Read on to find out which one does the best job.

Rounding ’em up
We’ll of course look at each of these PSUs in greater detail, but first, let’s set the stage with a wider view of how they compare. Many important attributes make up a good PSU, and we’ve crafted a simple comparison chart that summarizes some of the basics for the models we’ve assembled.


Wattage

Cooling

Modular?

80 Plus?

Warranty

Price
Corsair HX750W
750W
750W 140 mm bottom Yes Silver 7 years
Enermax
Revolution85+ 850W
850W 135 mm bottom Yes Silver 5 years* $219.99
Seasonic X
Series 750W
750W 120 mm bottom Yes Gold 5 years $179.99
XFX Black
Edition 850W
850W 135 mm bottom Yes Silver 5 years

As you can see, we’re looking at 750 and 850W units. Corsair and Seasonic will square off at 750W, while Enermax and XFX will do battle 100W up the line. Don’t put too much stock into these total output ratings, though. Each PSU divides its power differently, and where the watts flow is arguably more important than the sheer number available.

But what about the fact that we’re testing 750W units against others with a 100W advantage? Worry not, because our testing methodology is designed to take into account such differences. In addition to putting each PSU inside a real system, we’ll be probing its performance at 25, 50, 75, and 100% of its rated capacity.

A power supply’s efficiency is one of its most important attributes and something we’ll test ourselves in a moment. However, the 80 Plus program also provides efficiency certifications for the industry. Three of these four units are 80 Plus Silver certified, which means they achieved 85-88% efficiency in the tests conducted by the program. Only the Seasonic X Series has an 80 Plus Gold rating, denoting an efficiency of 87-90% in the program’s standardized tests. You can view the 80 Plus testing protocol here (PDF).

The energy lost due to less-than-perfect efficiencies generates heat that must then be expelled from the PSU. All the models we’ve gathered employ bottom-mounted fans, but the sizes of those fans range from 120 to 140 mm. Interestingly, what should be the most efficient PSU also has the smallest fan. In a moment, we’ll see how these slightly different approaches to PSU cooling affect system temperatures and noise levels.

We can easily measure degrees and decibels, but quantifying a PSU’s longevity is considerably more difficult. A good power supply can last for years, persisting through multiple upgrade cycles in a primary system before ending its days tucked away in a closet file server. We can’t test for long-term durability and still produce reviews in a timely manner, but we can get a sense of how long each company will stand behind its product by looking at warranty coverage. Seasonic and XFX both cover their PSUs for five years, which is about standard for high-end enthusiast models. Corsair kicks in an additional two years of coverage for the HX750W, while Enermax skimps with a three-year warranty.

The Revolution85+’s shorter warranty would be easier to forgive if it were one of the more affordable models, but it’s actually the most expensive by $30. The Corsair, Seasonic, and XFX units are all priced within $30 of each other, with the HX750W ringing in as the most affordable of the bunch.

*Update 01/15/10 — Enermax has decided to extend the warranty coverage on a number of its PSUs, including the Revolution85+, to five years. What’s more, it seems that this very round-up may have inspired the change. Regardless of the motivation, we applaud Enermax for improving the Revolution85+’s warranty coverage.

Counting connectors
All of the units we’re looking at have modular cabling, but each offers a different assortment of plugs and connectors. We’ve untangled the mess and summarized the connector counts for each PSU below.


Main power

Aux 12V

PCIe

4-pin peripheral

SATA

4-pin floppy
Corsair HX750W
750W
20/24-pin 4/8-pin 4 x 6/8-pin 6 12 2*
Enermax
Revolution85+ 850W
20/24-pin 4-pin, 8-pin 4 x 6/8-pin 6 12 1
Seasonic X
Series 750W
20/24-pin 4-pin, 8-pin 4 x 6/8-pin 8 8 2*
XFX Black
Edition 850W
20/24-pin 4-pin, 8-pin 4 x 6/8-pin 8 11 2*

First, the easy stuff. All of the units have hybrid 20/24-pin primary power connectors, and they can all provide auxiliary 12V power with a four- or eight-pin plug. The HX750W’s auxiliary 12V line uses a hybrid 4/8-pin connector, while the others have separate plugs for each.

On the PCI Express front, four hybrid 6/8-pin connectors extend from each PSU. Official CrossFire and SLI certifications aside, you should be able to power a couple of high-end graphics cards from either camp with any of these PSUs.

Things get a little more interesting when we turn our attention to SATA and peripheral connectors. All but the Seasonic are biased towards SATA connectivity, with the Corsair and Enermax units offering twice the number of SATA connectors that they do Molex plugs. The Corsair and Enermax PSUs can make use of all the Molex and SATA connectors listed above. However, the Seasonic and XFX models don’t have enough modular plugs for all of their included cables. You’ll have to sacrifice two Molex or two SATA plugs with each PSU.

Floppy drives are rare these days, but PSU manufacturers still support their mini four-pin connectors. The Revolution85+ has a built-in floppy connector, while the others come with Molex adapters. Corsair’s adapter will cost you a single Molex plug for each floppy. The adapters included with the Seasonic and XFX PSUs are less wasteful, attaching two floppy connectors to a single Molex plug.

Cable reach
The number of connectors provided is only one part of a power supply’s cabling equation. How far those connectors reach is also important, especially if you’re running a larger tower enclosure or one of those exotic upside-down cases that puts the PSU below the motherboard. Even if you have a relatively small, traditional case, longer cables can provide more routing flexibility.

With the help of our trusty measuring tape, we’ve determined the maximum cable reach for each PSU. The measurements shown for SATA and four-pin peripheral connectors refer to the reach of the last connector on the longest cable.

Only a few inches separate the longest motherboard power cables from the shortest ones. Corsair provides the longest reach here, outstretching the Revolution85+’s cables by half an inch. The XFX unit’s primary power cable is a little on the short side, which could create problems in upside-down cases in particular.

The PCIe power cables provided by each PSU are closer in length than the motherboard power leads. Again, Enermax and Corsair lead the field.

Despite having the shortest primary motherboard power cable, the XFX Black Edition’s Molex and SATA plugs offer several more inches of leeway than the competition. Enermax pulls up particularly short when we look at four-pin Molex connectors, but at least it offers plenty of reach for SATA devices.

Rated capacities
We’ve already discussed the total output wattage rating of each of the PSUs in the spotlight today, but that’s only one component of the output rating story. Modern PSUs divide power across three main lines at 3.3, 5, and 12 volts, with each of those lines carrying a maximum current rating. As if that weren’t complicated enough, many PSUs also spread 12V power over multiple individual lines.


Maximum output current (Amps)


DC Output

+3.3V


+5V

+12V
Corsair HX750W
750W
25 25 62
Enermax
Revolution85+ 850W
25 25 30, 30, 30, 30,
30, 30
Seasonic X
Series 750W
25 25 62
XFX Black
Edition 850W
24 30 70

Of these four models, only the Enermax splits its 12V line between multiple rails—a whopping six of them, to be exact. The rest of the units consolidate their 12V power on single rails.

Don’t get married to these current ratings, though; they’re only the tip of the iceberg. To get a handle on each PSU’s true capacity, we have to determine the maximum output wattage of each voltage line. The math is easy enough thanks to Ohm’s Law, which allows us to calculate wattage given voltage and amperage. However, power supply units with multiple rails are typically limited by how much power can be spread across those multiple lines—a total that’s usually less than the sum of each rail’s output capacity. Most PSUs also place limitations on how much power can be shared between the 3.3V and 5V lines. And then there’s the maximum output wattage across the 3.3, 5, and 12V lines, which often falls short of the PSU’s total output rating in order to reserve capacity for lesser-used voltage lines like the -12V and 5V standby rails.

To make sense of it all, we’ve put together a table showing the maximum output power for each PSU’s 3.3, 5, and 12V rails. Where applicable, we’ve also indicated the maximum combined 3.3 and 5V power, the maximum combined 12V power, and how much wattage the PSU can spread across all three main rails.


Maximum output power (W)


DC Output

+3.3V


+5V

+12V
Corsair HX750W
750W
82.5 125 744
150
750
Enermax
Revolution85+ 850W
82.5 125 360, 360, 360,
360, 360, 360
160 840
850
Seasonic X
Series 750W
82.5 125 744
125
750
XFX Black
Edition 850W
79.2 150 840
150
850

Interestingly, the Corsair and Seasonic PSUs have identical output ratings for their individual 3.3, 5, and 12V lines. However, Corsair is more optimistic about how much power can be shared between the 3.3 and 5V rails. The maximum sustained output across all three rails is identical at 750W, though.

The Revolution85+ has a little more combined 3.3 and 5V capacity than the 750W units. About 100W of additional 12V output power is also spread over its half-dozen rails. That total 12V capacity neatly matches the XFX Black Edition, whose single 12V line can likewise handle up to 840W. The Black Edition actually has a less powerful 3.3V rail than even the 750W units, though. It also has less combined 3.3 and 5V power than the Enermax PSU.

As one might expect from a collection of high-end PSUs with loads of PCI Express graphics card connectors, there’s a clear bias toward 12V power. Each model is capable of reaching very close to its total output wattage on just the 12V line alone. CPUs and graphics cards demand more from the 12V line than any other component, a fact clearly not lost on these vendors.

Loading up The Beast
A cornerstone of our power supply testing methodology is a custom-built load generator created by forum regular just brew it! that we like to call The Beast. If you’re unfamiliar with its frightening array of resistors, I strongly suggest checking out this page from our first round-up to use The Beast, which details the rig’s internals and our testing methodology.

We recalibrated each and every one of the variable-load resistors inside The Beast prior to testing for this round-up. None of the resistors needed more than a minor adjustment, but since we did tweak things some, the results in this article aren’t directly comparable to those from our previous PSU round-ups.


Behold The Beast!

We use The Beast to push each PSU to 25, 50, 75, and 100% of its output capacity while measuring DC voltage, AC ripple content, and gathering data that can be used to calculate overall efficiency. This creates a kind of level playing field on which each PSU is pushed to its individual—and advertised—limits. We should note, however, that our testing methods are not identical to those used by the 80 Plus program or by vendors who publish their own efficiency ratings. The Beast is a different breed of load generator than those used by the folks at 80 Plus; it only taps the 3.3, 5, and 12V rails, leaving -12V and standby 5V lines unused. To ease confusion, we’ll be referring to efficiency ratings gleaned from our own testing as Beast efficiencies. Those figures shouldn’t be compared to efficiency ratings posted by PSU makers.

The Beast is also limited to applying loads in 2A increments, so we borrow a page from The Price is Right and use amperage loads that come as close as possible to our targets without going over. The chart below shows the amperage loads applied to each PSU.


Total loads (Amps)


25%

50%

75%

100%

3.3V

5V

12V

3.3V

5V

12V

3.3V

5V

12V

3.3V

5V

12V

Corsair HX750W 750W
2 2 12 6 6 26 10 10 38 14 14 52

Enermax Revolution85+
850W
4 4 14 8 8 28 12 12 44 16 16 58

Seasonic X Series 750W
2 2 12 6 6 26 8 8 40 12 12 52
XFX Black
Edition 850W
2 4 14 6 8 30 10 12 44 12 16 60

When testing with The Beast, each power supply was hooked up using its primary and auxiliary 12V connectors, and when available, two PCIe power connectors and six 4-pin peripheral connectors. We used a Pico ADC-212 digital oscilloscope to probe the 3.3 and 5V wires on the primary power connector. The 12V lines were probed at the primary power connector and also at one of the PCIe power connectors. In the graphs on the following pages, 12V power from the primary connector will be marked 12V1, while power from the PCIe connector will be marked 12V2.

Rather than calculating efficiency based on static 3.3, 5, and 12V, er, voltages, our calculations take into account the actual DC voltage delivered on each line during testing. This should compensate for any voltage fluctuations that some PSUs exhibit under load.

Our testing methods
Testing was conducted in two parts. First, the PSUs were run in the system detailed below for a series of power draw, temperature, and noise level tests. They were then hooked up to The Beast to test power delivery and overall efficiency.

All tests were run three times, and their results were averaged.

Processor

Athlon 64 X2 5000+ 2.6GHz
System bus HyperTransport
16-bit/1GHz
Motherboard

Asus M2N32-SLI Deluxe Wireless Edition
Bios revision 0906
North bridge nForce 590 SLI SPP
South bridge nForce 590 SLI MCP
Chipset drivers ForceWare 9.35
Memory size 1GB (2 DIMMs)
Memory type

Corsair CM2X512A-5400UL

DDR2 SDRAM at
742MHz
CAS latency
(CL)
5

RAS to CAS delay
(tRCD)
5
RAS precharge
(tRP)
5
Cycle time
(tRAS)
12
Audio codec Integrated nForce
590 SLI/AD1988B with 5.10.1.4530 drivers
Graphics
GeForce 8800 GTS 640MB
with ForceWare 162.18 drivers

Hard drives
2 x

Western Digital Caviar RE2 400GB
SATA

OS


Windows XP Professional

OS updates
Service Pack 2

We used the following versions of our test applications:

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.

Corsair’s HX750W 750W
A surprising bargain

Manufacturer Corsair
Model HX750W 750W
Price (Street)
Availability Now

Corsair’s HX620W took home a TR Editor’s Choice award in a massive 11-way PSU round-up some two years ago. Seeing Corsair come out on top in a round-up is hardly surprising; the company has been building quality enthusiast-grade products for years. However, the HX620W was the company’s very first power supply, making its excellent overall performance and smart feature set all the more impressive.

There are now 14 different models in Corsair’s PSU lineup. The latest to arrive in our labs is the HX750W, which, as you’ve astutely observed, has a 750W output rating. Among our group of four PSUs, the HX750W is the cheapest of the bunch by a good $20.

Despite being the most affordable unit in the pack, the HX750W doesn’t cut any corners. Heck, its seven-year warranty is the longest of the lot by two years, and Nvidia’s even blessed the unit with an official SLI endorsement. The HX750W sports the largest fan of the bunch, too—a variable-speed 140-mm fan occupies the unit’s bottom panel accompanied by plenty of venting at the rear.

PSUs rarely offer much in the way of visual flair, but Corsair’s use of matte black finish throughout gives the HX750W a stealthy look. I like the understated aesthetic, although you’re only going to see it if your case happens to have a window—and a tall one, at that.

More important than the HX750W’s choice of exterior colors is its modular cabling. The primary motherboard connector and auxiliary 12V line are the only cables you can’t remove from the unit. They’re also the only cables that you really can’t build a modern system without, so it doesn’t make much sense to have them modular, anyway.

All of the PSUs we’re looking at today have some degree of modular cabling. However, only Corsair does something original with the cables themselves. The blacked-out leads match the PSU’s Vader motif, and Corsair says their thin profiles are designed to maximize airflow within a system.

The HX750W delivered solid DC voltages across all four load levels we generated with The Beast. The 12V rail trends a little high and the 3.3V line a little low, but only by the slimmest of margins. We’re talking about deviations of less than one tenth of a volt here.

Regardless of the load level, the Corsair PSU’s AC ripple content remains flat at around 45 millivolts, which is well within tolerances.

Under our Beast-generated loads, the HX750W never dips below 89% efficiency. Impressive, especially when you consider that the PSU’s efficiency doesn’t change by more than a percentage point across our 50, 75, and 100% loads.

Enermax’s Revolution85+ 850W
Talkin ’bout a revolution

Manufacturer Enermax
Model Revolution85+ 850W
Price (Street) $219.99
Availability Now

With a $220-280 street price, Enermax’s Revolution85+ is the most expensive PSU in this round-up. We’re not averse to pricey hardware here at TR, just so long as you’re getting what you paid for. The question for the Revolution85+ is a simple one, then: is it worth the extra scratch?

At first glance, one might be inclined to say no. Sure, the Enermax brings 100W more than the Corsair and Seasonic units. However, the XFX Black Edition also packs 850W, yet it’s at least $30 cheaper. You’re not paying a premium for additional warranty coverage, either. The Revolution85+’s three-year warranty looks positively stingy next to the five- and seven-year coverage offered by the competition.

Update 01/15/10 — Enermax has decided to extend the warranty coverage on a number of its PSUs, including the Revolution85+, to five years.

Dive a little deeper into the Revolution85+’s design, and you can see why Enermax might be inclined to charge extra. Most high-end PSUs these days consolidate their 12V power on a single rail, but Enermax spreads it across half a dozen lines, a design the company claims offers the best safety and compatibility. The PSU’s dedicated 3.3 and 5V DC-to-DC conversion circuitry is said to offer better efficiency than generating 3.3 and 5V power with a transformer, as well.

The Revolution85+ also supports zero-load states on all of its rails. This capability is apparently necessary for future CPUs that will employ ultra-low-power C6 sleep states and upcoming graphics cards that will offer “hybrid” hibernation modes that cut power substantially.

Even the Revolution85+’s variable-speed fan has received special attention. A small lip on the fan’s frame is designed to reduce turbulence, which should lower noise levels. Another nice touch: the fan will keep running for 30-60 seconds after a system is powered down to ensure that hot air doesn’t stagnate inside an enclosure once the case fans stop spinning.

The Revolution85+ has a textured, almost speckled finish that’s unique, if nothing else. I like the indentations on the side panels, although again, you’ll never notice unless you happen to have a case window. You will notice the status light at the rear, however. It glows in three different colors to indicate normal operation, standby mode, and failure.

From here, we can also see a healthy dose of ventilation on one of the PSU’s internal panels. This is the only model in the bunch that offers internal and external ventilation holes.

Most of the Revolution85+’s cables are modular, but the primary motherboard, auxiliary 12V, and two PCIe power connectors are not. If you’re building a system and don’t need at least two power cables running down to PCI Express graphics cards, you probably shouldn’t be using an 850W PSU.

Although Enermax sheathes all of the Revolution85+’s cables, it leaves a rather large gap between the sheathing and the first plug on each line. There’s no sheathing between multiple connectors on a line, either.

DC voltages are nice and stable on the Revolution85+, and very close to the target value for each line.

The Revolution85+ keeps its DC lines relatively free of AC ripple content. We’re looking at only about 50 millivolts of AC content here.

Interestingly, the Enermax unit’s Beast efficiency peaks under a 75% load, just topping 89%. The Revolution85+ does no worse than 86%, reaching that mark under our lightest load.

Seasonic’s X Series 750W
One of its very own

Manufacturer Seasonic
Model X Series 750W
Price (Street) $179.99
Availability Now

Seasonic is one of the largest PSU manufacturers around. In fact, Seasonic builds PSUs for a good number of other firms that then sell those units under their own names. The X Series is Seasonic’s very own product, though, and its most advanced model to date. This is the first power supply we’ve tested with 80 Plus Gold certification, too—the highest standard the program sets for ATX PSUs.

The X Series carries a bit of a premium thanks to its Gold certification; the 750W model costs $20 more than Corsair’s HX750W. The Seasonic unit is also considerably harder to find online. Our price search engine doesn’t list it, but Newegg does have units stock, with free shipping, to boot.

Seasonic PSUs have never been particularly flashy, and neither is the X Series. The combination of matte black with gold trim reminds me a little of old-school stereo equipment for some reason. The look is a classy one, although there’s less of it, simply because the X Series is the shortest PSU of our pack by about an inch. None of the PSUs in this round-up are too large to squeeze into most mid-tower cases, though.

Perhaps because the X Series has a smaller casing, Seasonic uses a Sanyo Denki San Ace fan that measures just 120 mm across. This is the smallest fan in the bunch. Still, given Seasonic’s pedigree, it’s hard to question the decision. Seasonic’s focus seems to be on lower noise levels, which is why the fan doesn’t spin up at all until the PSU is loaded up to at least 20% of its capacity. From there, the fan spins at a constant “silent” speed until the PSU load reaches 50%, at which point the fan really starts to ramp up.

Internally, the X Series uses a patented DC connector module with an integrated voltage regulator that the company claims offers “near perfect” DC-to-DC conversion for 3.3 and 5V power. According to Seasonic, this design allows the PSU to run lower currents to supply its 3.3 and 5V lines, reducing loss and improving overall efficiency.

All of the PSUs in this round-up may be modular, but the X Series is the only one that’s completely so. Each and every one of its cables, including even the primary motherboard connector, can be completely detached.

While this arrangement may offer questionable utility for end users who are probably always going to need a primary motherboard and auxiliary 12V line connected, the lack of attached cables does make the X Series a little easier to squeeze into tighter enclosures. The cables are nicely sheathed, too—not just down to the first plug on each line, but in between the subsequent ones, as well.

The X Series 750W offers consistent DC voltage delivery that’s well within the company’s +/- 3% tolerances.

AC ripple is low, as well, averaging about 50 millivolts across all rails and load levels.

Like the HX750W, the Seasonic X Series is most efficient under the lightest load generated by The Beast. There’s little difference in efficiency between loads at 50, 75, and 100% of total capacity.

XFX’s Black Edition 850W
Another one jumps onto the bandwagon

Manufacturer XFX
Model Black Edition 850W
Price (Street)
Availability Now

For the most part, we’ve seen a great deal of consolidation in the PC market in the last few years. The PSU market, however, has exploded with new entrants. The latest player to throw its hat into the ring is longtime graphics card maker XFX, which is starting at the high end with the Black Edition 850W. Go big or go home, I guess.

Speaking of going big, XFX has gone with quite a bold design for its very first power supply product. The slate-gray enclosure has lots of angular detailing, especially around the fan guard, which seems to be inspired by a spider’s web. Behind the guard lies a 135-mm cooling fan that’s been dipped in an apparently radioactive shade of lime green. There’s a real sense of distinctive industrial design here, and while it’s not the sort of look I want in my living room, it should fit right in within the confines of a high-end gaming rig.

The Black Edition has the perfect color scheme for SLI certification, which it boasts alongside a CrossFire-ready badge. Energy Star 4.0 certification also solidifies this PSU’s, ahem, green credentials.

With the aid of DC-to-DC voltage regulator modules for the 3.3 and 5V lines, XFX says that the single-rail Black Edition offers up to 90% efficiency. The PSU’s advertised voltage tolerance is +/- 3% for all rails, which is pretty standard for high-end units.

XFX has wisely gone the modular route with the Black Edition, and it leaves the primary motherboard, auxiliary 12V, and two PCIe power connectors permanently tied to the PSU. Even the modular connection panel has some subtle cosmetic detailing, complete with another shot of that neon green.

The modular cables are a little more run of the mill. They’re sheathed nicely in black, but look like they could’ve been built for any other PSU. I suppose you can’t have everything, especially when this 850W unit costs just $10 more than the Seasonic 750W. And XFX delivers where it counts, serving up the five-year warranty one expects from a premium power supply.

Even a budget PSU should deliver impeccable DC voltages, and the Black Edition has no problem on that front.

The PSU’s AC ripple content is also minimal, hovering around 50 millivolts like all the other units we’ve looked at today.

The Black Edition does even better on the efficiency front, hitting nearly 98% when subjected to the lowest load generated by The Beast. Once more, we see the Beast efficiency level off across 50, 75, and 100% loads.

Efficiency
We don’t want to make too many direct comparisons between test results gathered from The Beast, because each PSU was run under different loads corresponding to its individual specifications. However, efficiency is important enough to make an exception. Here we’ve graphed the efficiencies of each PSU at 25, 50, 75, and 100% capacity to see how they stack up against each other.

Yeah, so these PSUs are all pretty efficient when connected to our load generator. The Seasonic and Corsair units fare the best overall and offer nearly identical efficiencies across all four load levels. The Enermax and XFX units aren’t far behind, either.

Only the Revolution85+ fails to reach its highest efficiency with our lightest 25% load. Interestingly, it’s also the only one that uses multiple 12V rails rather than a single beefy one, which could be responsible for what we’re seeing here.

System temperatures

Our next batch of tests deployed the PSUs in a real-world system with a pair of GeForce 8800 GTS cards in SLI and a couple of hard drives. For these tests, the systems first sat at idle for 10 minutes. They were then subjected to a 10-minute load consisting of Prime95, Oblivion, and an IOMeter file server test pattern. Finally, the systems were allowed to idle for a 10-minute cool-down period.

System temperatures were measured using Everest Ultimate Edition.

At idle, the Seasonic PSU seems to be doing the best job of keeping the chassis cool, which is somewhat amusing considering that it has the smallest fan of the bunch. The HX750W isn’t far behind, but the Black Edition doesn’t appear to be moving nearly the same amount of air as its competitors.

The Black Edition registers the highest system temperatures under load, too. The others are a little more closely matched, with the Enermax offering the lowest CPU temperatures and the Corsair keeping our motherboard the coolest.

After ten minutes of cool-down, the field actually looks pretty even. The Revolution85+ cools the CPU faster than any of the other PSUs, and even the Black Edition drags itself into first place in motherboard temperatures. However, the XFX PSU still leaves our system’s hard drives a few degrees warmer.

Noise levels
Noise levels were measured at idle and under load using a TES-52 digital sound level meter placed 1″ from the rear of the system and out of the direct path of airflow.

Only a couple of decibels separate the field at idle, with Seasonic and Enermax tying for the lead. The HX750W is the loudest of the lot here, although not by enough of a margin that my ears noticed the difference.

The spread shrinks down to just over a decibel under load, and although the HX750W redeems itself according to our sound level meter, it’s very difficult to actually hear differences in noise levels this small. None of the fans have high-pitched or otherwise annoying noise characteristics, either.

Power consumption
Power consumption was measured at the wall socket for the entire system, sans monitor and speakers.

Our 850W units predictably draw more power than the 750W ones, particularly at idle. However, those differences shrink under load, where we’re only looking at a five-watt spread. Corsair and Seasonic trade the lead at 750W, while Enermax seems to have a more consistent edge over XFX at the higher wattage.

Conclusions
Round-ups like this one can be difficult to judge because we looked at four very competent competitors today. Each and every one of them has modular cables and plenty of connectors, including four 6/8-pin PCI Express plugs. Power delivery was excellent across the board, with tight DC voltage tolerances and very little AC ripple. For the most part, all the units were plenty cool and quiet, too.

I wouldn’t have reservations about running any of these units in my own systems. However, I do think that some are better than others, especially when you consider overall value.

The most questionable value in the bunch is Enermax’s Revolution85+. With a $220 street price, you’re looking at about a $30 premium over the XFX Black Edition. Granted, I think Enermax has a little more going on under the hood with support for zero-load states on all rails. But the measly three-year warranty simply isn’t good enough when less expensive competition gets at least five years of coverage. And the competition does a better job of cable sheathing, too. With the Revolution85+ offering largely equivalent performance to its rivals, it’s difficult to justify the price premium for what is otherwise a great PSU.

Update 01/15/10 — Enermax has extended the Revolution85+’s warranty coverage to five years, improving the PSU’s value proposition substantially.

Part of what makes the Revolution85+’s price so hard to swallow is the fact that an XFX Black Edition with the same output rating costs only $190. I love the design direction XFX has taken here, and for a first entry into the market, the Black Edition is a very solid PSU. There is room for improvement, though. The ultra-long Molex and SATA cables are great, but the Black Edition needs some more length on its primary motherboard and auxiliary 12V lines. Based on the higher system temperatures we observed, the fan profile could use some tweaking, too. Otherwise, the Black Edition offers good value for a high-wattage PSU.

Seasonic’s X Series may have a capacity rating 100 watts lower than the XFX and Enermax units, but it should still be capable of powering a high-end system. 80 Plus Gold certification doesn’t come cheap, of course, but the unit’s $180 street price is reasonable considering its low noise levels and power consumption. The completely modular design is also an interesting twist, although I can’t see it delivering any actual benefits in a real-world system unless you’re using the X Series as a secondary PSU to power peripherals or graphics cards exclusively. Still, of all the PSUs in this round-up, the X Series is the one I’d pull off the shelf to build a system with right now just because it’s slightly quieter than the others.

Corsair HX750W
January 2010

With that said, it’s not the PSU I’d go out and buy with my own money. That would be Corsair’s HX750W, which rings in $20 cheaper than the Seasonic yet offers an additional two years of warranty coverage. The HX750W’s performance is comparable to that of the Seasonic unit, but its cables are longer, thinner, and more plentiful overall. Yes, the HX750W’s idle noise levels are a couple of decibels higher at a distance of 1″, but put my ears a couple of feet away, and they don’t notice a difference. While it may not be the most interesting or exciting PSU in the bunch, the HX750W does offer the best mix of features, performance, and value. That earns it our coveted Editor’s Choice award.

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