A good power supply doesn't just provide you with ample output. Increasingly, vendors have put a bigger emphasis on delivering power more efficiently, too. We're testing five 80 PLUS Platinum-rated power supplies in the 550- to 600-watt range.

While Citius, Altius, Fortius, or faster, higher, stronger is the motto for the Olympics, the PC powersupply market also follows this adage fairly religiously. Manufacturers continue to leapfrog each other by enabling increasingly higher outputs to cope with the most aggressively overclocked CPUs and multi-card graphics configurations drawing hundreds of watts.

For this round-up of efficient desktop power supplies, we asked power supply manufacturers to send us their 80 PLUS Platinum-rated products at the lower end of the output spectrum. We set the upper limit at 600 W. Any lower and the number of contestants would have been too small. Our objective was to help system builders find an efficient solution for single-graphics card gaming and other moderately-demanding applications. Five companies submitted samples: the AntecEarthWatts Platinum 550 W, Cooler Master Silent Pro Platinum 550 W, Enermax Platimax 600 W, Kingwin Lazer Platinum 550 W, and Rosewill Fortress-550.

Naturally, the 80 PLUS Platinum rating costs more to procure. But although the output of our five test candidates only varies by 50 W, their price differences turn out to be quite a bit more significant. The list price of Antec's unit is only $120, the Enermax asks you to pay as much as $190! The Cooler Master and Kingwin power supplies are both listed at $170, while Rosewill's sells for $140. Keep in mind that we're citing each manufacturer's suggested price; the actual prices of these power supplies are often up to 20% lower.

It gets bad enough that a cyber-stroll through Newegg or TigerDirect gives you the impression that power supplies under 500 or 600 W aren't even worth looking at. After all, if a fairly affordable card like the Radeon HD 7950 requires at least a 500 W PSU, according to AMD, then adding an overclocked CPU and some storage necessitates even more, right? Fortunately, even as the power supply vendors crank up output, they're simultaneously improving the efficiency of their highest-end offerings.