With a case ordered and a CPU in mind I decided to focus on the power supply next. Remember that the better cases come with fans but not with a power supply (and in general that’s good, you want to pick you own).

As I did the reading I found it’s more complicated than it seems. Ideally you know what the power demand is before you buy. Too small and you’ll end up having to buy again, too big and you waste money (and maybe power, it depends). Knowing how much power means figuring out the whole inventory, which I wasn’t quite ready to do (perhaps illogically).

I can tell you that the I7 I planned to get was going to need a max of about 80 watts. After that the biggest consumer of power tends to be the add-in graphics card. Drives and fans use some, but not nearly as much. That’s a generalization, but I think a fair one. The lower end of the power scale is usually in the 400w range and that seemed about right, so I started reading those reviews.

I learned that good power supplies are rated as 80 Plus, meaning they are 80% or more efficient at various points between 20 and 100% utilization. There are grades above that, but for this build I didn’t think it made sense – it may start to if you’re running a 1000w or higher (1 kilo-watt hour per hour) system 24×7, or if your energy costs are higher than mine (I think around .08/kwh).

All of them come with the basic cables to power the motherboard, CPU,a fan,and a couple SATA drives, and probably one PCI Express cable for graphics cards that need more power than it can get from the slot. Bigger power supplies come with more cables, which you then have to manage – as in organize and push out of the way. Top end devices have modular plugs so you can only use the cables you need.

If you want to learn more, try here and here.

I started with the Corsair 430, an 80 Plus model. Unboxing it I was struck by how nice it was. All the cables are enclosed in braided sleeves and the whole thing felt solid. Installing in the case was easy enough, four screws that go through the back of the case (and come in the box). The case has a bottom air vent just for the power supply, including a slide out air filter which seems like a nice feature. The cables are clearly labeled too.

Powering it up with no load it was quiet. Very quiet. So far so good.

Later I ended up trading up to a 500w model only because it was on sale and I wanted to replace the power supply on my old machine. The 500w one came with two PCI-E cables, neither of which I’m using so far.

I spent about $40 for each of them, and there are several competitors that are priced in the same range. If you’re not going to use a big dog graphics card the 400w size works fine, no reason to tie up money that you can use for something else. Replacing it later – which I went through when I changed to the 500w – was less than 10 minutes, easy work provided the case gives you some room to work.