Dude you got a Dell...me to
So what model do you have. Before you go slappin in a PSU, coupla questions need to be answered. Which Dell, is it ATX or BTX form factor. If you have the 6800 gs I am guessing you have a 350 -375 watt PSU with probably 28-30 amp dual 12v rails. The PSU may be sufficient depending on how much hardware you have.
If you are looking at the front of the tower...which side panel do you access the internals from? Left side =ATX, right side =BTX.
Do you have an open back chassis, if not you will have to cut a kill switch hole, that is if you get a PSU with a kill switch.