I suppose the assumption is that all power supplies of similar wattage are created equal, but that couldn't be farther from the truth. PC power supplies can differ in not only more obvious environmental attributes like noise and heat levels, but also in the quality of power they deliver.

Last year, I compared four different power supplies from Antec, Thermaltake, and Vantec. Antec's TruePower line came out as our Editor's Choice in that comparison by delivering tight DC voltage tolerances with low noise levels. Today, I've rounded up five brand-new power supplies from Ahanix, Antec, Enermax, Vantec, and Zalman to compare with each other and our previous favorite. I've updated our power supply testing gauntlet, too. Not only will we be looking at DC voltage tolerances and noise levels, we'll also take a peek at each power supply's impact on system temperatures and measure its AC ripple voltage.

Which power supply stands out from the competition as being the quietest, coolest, and cleanest source of PC power? Read on to find out.

The specs
Power supplies are usually bunched together based on their total output wattage, but there's more to wattage than total output. Today we're dealing with 400 and 550W power supplies, and there's quite a bit of variety when it comes to distributing that total wattage over available voltage lines.

While Enermax, Vantec, and Zalman's power supplies all share voltage between the 3.3 and 5V rails, Antec's TruePower and TrueControl models have dedicated output circuitry for each rail. This dedicated output circuitry comes in handy when a system has an unbalanced overall load that's biased towards the 3.3 or 5V line. If the 3.3 and 5V lines don't have to share wattage between them, each line can be loaded to its theoretical limit.

Overall, Enermax's EG651P-VE(FMA) offers more wattage on the 3.3 and 12V rails than any other power supply we're looking at today, but only 180W on the 5V rail. Ahanix's SilenX is a little weak on the 3.3V line, but its maximum 12V wattage is quite strong. Vantec and Zalman's offerings, on the other hand, offer relatively low 12V wattages but plenty of power on the 5V line.

For reference, here are the maximum output currents for each power supply's output lines:

Other than Enermax, whose EG651P-VE(FMA) offers the same maximum amperage on the 3.3, 5, and 12V lines, manufacturers tend to offer higher currents on the 5V line.

Theoretical specs are only so exciting, so let's dive in and take a closer look at what each power supply has to offer.