dell PSUs are not that inferor as you believe them to be. they are actually decent PSUs. of course there are better ones out there, but they are enough for most people's needs.
i own a dell dimension e520 with a 305W PSU and it has two 12V+ rails both rated at 18A. most computers don't even use that much total watts. if you look at all the computers with Q6600 processors, raptor harddrives, 8800gt's, and other devices. they don't even use more than 400 watts and most of the time below or around 300 watts. my computer specs are a e6420 processor, 2gb ddr2 ram, 320gb harddrive, dvd burner, hd 3850 videocard, and an audigy 2 soundcard with the standard dell PSU. i haven't had any blue screens of death and playing graphic intense games (bioshock, call of duty 4, crysis) haven't caused me any problems.
so if i am able to run a hd 3850 videocard on my dell computer. i don't see why you cannot run a 8600gt or a 2600xt on your dell computer.
most likely we have the same PSU.