The bigger issue I think is what the amount of power on each of the rails is when you get down to 120W, not so much whether you are actually drawing 120W. Having a power supply that small means that if the rails aren't allocated properly, you could be missing power in one critical area and be underpowered on a single rail causing issues. Not sure what a E4300/4400 or 6550 would draw on each rail even if on a uatx board your total draw is under 120W. Not saying it wont work, just saying you should look into it a bit further before making any purchases.