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Four killer PSUs go head to head

A new battle at 750 and 850W
— 9:22 PM on January 14, 2010

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.