One easy and quick way to judge the quality of your power supply is to pick it up and see how heavy it is. The heavier a power supply is, the bigger the heat sink inside, and usually other components are top notch as well. (to be sure, this should NOT be the ONLY way you judge a Power Supply, keep that in mind!).

If you have a flimsy little 300W power supply with a stamped air intake, and a single fan whizzing away at a high speed to keep it (and only it) cool, you need to ditch it. There are much better alternatives.

Quiet Power Supplies

There are two kinds of power supplies geared toward the silent user - those with low speed/controllable fans, and those without fans at all. I have to tell you now that fanless power supplies are tricky business. I'll get to that later though.

For now, have a look at this beauty from Antec. The Phantom is a 500W unit, for those with beefy video cards. What makes it so 'phantom-like'? The fan will only engage when it has to. Yeah, yeah, I've heard that before. No-name "silent power supplies" from China are silent for about 5 minutes, until the heat builds up, and the tiny fan whirrs to death, causing deafness to anyone within 100 yards. Nope, the Phantom can be set to engage the fan at three different settings; 40, 47.5, and 50 degrees. You can guess where I set it ;)

And when it DOES engage, it starts at a nice, low, quiet pace. It only ramps up to about 20 dBa. Not entirely silent, but quiet and reliable.

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Fanless Power Supplies

As mentioned above, fanless power supplies are sketchy at best. There's a reason a lot of companies like Thermaltake all but abandoned their fanless PSU products. The main reason is that the fan in the PSU is there for to help rid of all the heat the PSU itself is subjected to, from components within the case. This is especially the case with silent systems without any exhaust fans. In order for a power supply to be reliable without a fan, it has to be very efficient, and be designed to run under extreme stress. There is only one power supply that I know of that falls within this very slim category:

Want to know a little secret? This "300 watt" power supply is actually under-rated. Now there's something new! Silverstone's secret to success with the ST30NF is to use a hard core efficient 500 watt power supply unit, encase it in a highly effective aluminum heatsink, and rate it for 300W. That is why this is the only one I would trust to run in silent mode. Even though it can run at 500W no problem, it can't do it without a fan. At 300W though, no problem. This is the unit for you, if you're running a lower power system.

Keep in mind that having sufficient airflow is quite important in a silent PC, because you're likely to have very few fans on the individual components. Your CPU and your Video Card are going to heat up the case something fierce, and you need to expel that heat. Usually you would count on the power supply to help out, but remember that these are low noise power supplies, that move very little air. You ARE going to need a fan or two in your case, and you will have to pay close attention to what you put in there, and what kind of case you use.

Speaking of which, now's the time for us to discuss PC cases, and what kind you need to maintain a silent PC!