Do you really understand your power consumption needs on your system? Think that your 250 watt power supply on your Dell or Gateway might have a "skimpy" 12V rail that's totally maxed-out to your processor? Check this very informative article out for an answer: It certainly helped me! http://firingsquad.gamers.com/guides/power_supply/default.asp
Good power supplies are cheap. Get a good one with lot's of power. Built my PC over a year ago, and put in an Anatech TruePower 430 watt. It was under a hundred bucks, can't go wrong with that.
cannot obtain anything from Antec cause it doesn't fit. For your Dell, try this: http://www.pcpowercooling.com/products/power_supplies/index.htm