I had to buy a new power supply when I got my radeon x800pro. Older cards, atleast ones I've had, didn't attach directly to the power supply. New ones usually have a plug on them so the power supply hooks up directly to the card to run the fan and stuff. If your stock power supply doesn't have an extra hook up then you'll need a new one. Plus it's better to have available extra power to your components than to run them under-powered.