How I Tested

Confusion reigns in PSU marketing, so I set out to clear the air with some harsh, real-world tests. I mounted and ran each unit in a closed case—not on an open-air bench—under stressful operating conditions.

I used a test system with the following configurations:

A: 2x FX-74, 2x 8800 GTX SLI (8XAA/16XAF)

B: 2x FX-74, 1x 8800 GTX (8XAA/16XAF)

C: 2x FX-74, 1x 8800 GTS 640MB (2XAA/8XAF)

D: 2x FX-74, 1x 7900 GTX (2XAA/8XAF)

All configurations featured the following: 3GHz processor speed, 4x 1GB Corsair CM2X1024-8500C5D Dominator DDR2, two Raptor 10,000rpm hard drives, one WD 7,200rpm drive, two Sony DVD drives, one floppy drive, Asus’ L1N64-SLI WS (nForce 570 SLI) mainboard, ForceWare 97.92 drivers, and a Dell 3007WFP display at 2,560 x 1,600.

Systems C and D didn’t have enough video RAM to run 8XAA/16XAF at 2,560 x 1,600, but 2XAA/8XAF worked. I used Windows XP SP2—fully patched—as I didn’t want any instability attributed to incompatibilities between my software and Windows Vista. PC Wizard 2006 reported the system temperatures.

Not every power supply could handle a top-end system, so I varied the graphics card configuration to get a rough idea of each unit’s capabilities. Torture-testing a PSU via this method is basically like using a go/no-go gauge. You want a power supply that will easily handle your current system build and, ideally, your next one, too. But it will either work stably under a heavy, continually changing load, or it won’t. If a PSU didn’t have enough 6-pin PCI-E connectors, I used adapters from one of the video cards’ retail bundles.

I continuously looped 3DMark06 1.1.0 as individual instances of Prime95 ran on all four CPU cores using the In-Place Large FFTs Torture Test. The idea was to maximize the test PC’s power draw by utilizing as much of the CPU and GPU(s) as possible, with the RAM, hard drives, and motherboard core logic getting a workout along the way. 3DMark also provided variation in load to better test transient response. I noted the beefiest configuration each PSU could reliably run between two to four hours (I’d like to have tested each unit for several days) in the “Tested Stable To” row of the accompanying chart.

In configuration A, this truly hungry system sucked a maximum of 865W under load depending on the power supply, according to my Extech 380803 power analyzer. You know, your basic PSU’s nightmare.

I hadn’t planned for my computer case to add to the PSUs’ (and my own) torture, but it did. Thermaltake’s Armor Extreme doesn’t let you pull a power supply out the back like any sensible case; you have to move it through the front drive bays. Even more egregiously, Thermaltake decided to turn the PSU on its side and put a hard drive cage next to it. This not only places the weightiest components in the upper rear of the case (although it does allow the hard drives’ fan to evacuate heat) but also makes fan-side power harnesses several inches shorter. Most damningly, it causes the hard drive cage to block any bottom-mounted PSU fan that would normally face the CPU(s). On the bright side, this setup allowed me to test affected PSUs under horrible ventilation conditions.

One thing I dropped from my testing was direct measurement of the voltage level ranges. Like the Nvidia 680i Evga motherboard I’ve used earlier, my Asus nForce 570 SLI board didn’t report its +12V and +5V voltage levels. Also, my inexpensive digital multimeter exhibited voltage variation even at baseline, so I’d have to call my hands-on measurements inconclusive. In the end, I reasoned that any components running too far out of spec would make themselves known through instabilities. I certainly didn’t want anyone to base a buying decision on such questionable data.

PC Power & Cooling Silencer 750 EPS12V Quad

Silencer 750 EPS12V Quad
$199
PC Power & Cooling
www.pcpower.com
CPUs: 4

PC Power & Cooling is very pointed about why it believes its power supplies are superior. Founder Doug Dodson built industrial power supplies for harsh environments for nigh on two decades before turning his expertise to the consumer PC market, and it shows in the company’s products.

Big capacitors on the input side can better survive momentary power losses and brownouts (holdup time). Big capacitors on the output side offer stability under sudden load changes, such as when F.E.A.R. gets graphically intense (transient response). A rear fan doesn’t take away space for big heatsinks like a bottom fan would. Inductors and capacitors carry high temperature ratings, such as 105 C. All PCP&C units are tested in a 40 C oven at a 110% of maximum load at 90V instead of 110 to 120V, which means the PSU has to draw more current (and endure more heat) to supply the same wattage.

Thus, it’s not surprising that this PSU supports “all CrossFire setups, including new products that are shipping this spring.” I confirmed that all R600 variants are included in this pronouncement. At $199, this is a best buy indeed.

PC Power & Cooling Turbo-Cool 1KW SR

Turbo-Cool 1KW SR
$499
PC Power & Cooling
www.pcpower.com
CPUs: 4.5

It’s probably the best you can get, but you’ll pay for it. At half a grand, this PSU retails for more than most of us have ever spent on a graphics card. Heck, I’ve seen entire PCs for less.

This single-rail über PSU is long, both in case dimension and generous cable length. If you don’t have 11.5 inches between the back of your case and your bay-mounted drives, don’t bother. The company throws in some 6- to 8-pin PCI-E adapters, so you won’t have to worry should your wallet have enough cash left over for an R600.

There are cheaper alternatives with more connector flexibility. Many of them may offer service that’s just as reliable and long-lived. But if you want ample headroom for overclocking and future upgrades (not to mention world-class stability), consider this unit an investment.
Watt, Me Worry?

PC Power & Cooling’s 1KW SR is the top dog here, but you can’t rule out the Enermax Galaxy DXX 1000W and Cooler Master Real Power Pro 1KW for $130 to $180 less. For power on a budget, get the PCP&C Silencer 750 and never look back.

by Marty Sems