I am still trying to figure out which power supply to buy, and whether to go with a 90w or a 150w PSU. The online power simulators seem to say I can get by on 90w, but I want to be sure.

I am planning to buy a used 90w power supply (can get one for under $20 for sure). Since I have 2 or 3 different motherboards I might use, I was going to test different setups and see how the perform in my apartment before I settled on a PSU.

Are there any major flaws in that reasoning? Is Is there some material difference between a used 90w PSU and an Opus 90w as far as the actual power being supplied to the motherboard?