The important bit in choosing a power supply for a PVR type box is that it has to be as quiet as possible. A few quick searches showed that there were a handful of companies that were highly regarded and made some very quiet power supplies.
I wound up getting a Seasonic S12 330 watt power supply. And, sure enough, it sounded completely silent, at least out of the case. Inside the case I’m hearing a little fan noise, but I haven’t figured out what fan is doing that yet.
The Seasonic has a relatively large 12cm fan, which means it doesn’t need to spin as fast to move as much air as a smaller fan, which is a very good thing.
I didn’t have huge power needs; the video card is a relatively low end one that doesn’t need extra power. I’m only planning on having one hard drive in the box at any time, and figure if I need more space I’ll do that over the network. Adding more and more hard drives to the set-top box itself just seems like a guarantee that it’ll be getting louder than I want it to. So that’s why I went with 330W rather than something larger.
So, there’s the power supply. That was one of the easier choices in building the box.