i have a dell 4700 and i would like to upgrade the graphics card from a ati X300 SE to either a 6800 GS or GT. will my powersupply work with either of them and is there any videocards that will work with my powersupply. my powersupply is a 305 watt dual on the 12v rail with 18A on each rail. will i be able to upgrade to any videocard at all or not.