Okay one area in computer hardware I've always been suspicious of my knowledge is the power supply. I know the current common power supplies are of type ATX but from there I'm lost, mostly since I've never once had to change one. Well now I do...

I got two comps, both using ATX, however one comp's power supply was broken and thrown out before I got ahold of the comp. I am only guessing it is ATX since power supplies with ATX on the side are the only ones which have the same 24-pin plug.

How on earth can I determine if one ATX will work with another mother board? This is power we are dealing with, the last thing I want to do is feed the cpu a few extra...

Any advice?