| From: Kevin Cozens <kevin@ve3syb.ca> | Any spec for a video card as to power supply wattage would be a minimum. Not in my (limited) experience. I have bought cards that wanted to specify how big my system's power supply was because the actual required arithmetic is too hard for customers. They just guessed at what the rest of my system would require and left a margin for error. The real specs are a little tricky in theory (I don't actually know what things are like now). The power supply supplies various voltages, each with its own current limit. Each voltage is provided on one or more "rails", each with its own limit. But sometimes a maximum draw on one reduces the limit on another rail. You need a power supply that has enough oomph on each rail. So you want a requirement specified for each voltage. And generally you don't know how much power the rest of your system uses in aggregate. Usually when you build your own system you buy more power supply capactiy than you need. It doesn't cost too much more and you don't really know what's needed. I imagine that common garden variety computers from big manufacturers tend to size their power supplies with smaller margins.