Power Supply:XFX 550W 80+ Bronze Certified ATX Power Supply ($59.99 @ NCIX US) Total: $59.99 (Prices include shipping, taxes, and discounts when available.) (Generated by PCPartPicker 2014-01-28 14:14 EST-0500)
It would have to be a really high quality 500w PSU. Usually I wouldn't recommend anything less than a good 550w PSU for a 280x. Whats the make and model of the PSU. The specs for the system its being installed in would help aswell.
Power Supply:XFX 550W 80+ Bronze Certified ATX Power Supply ($59.99 @ NCIX US) Total: $59.99 (Prices include shipping, taxes, and discounts when available.) (Generated by PCPartPicker 2014-01-28 14:14 EST-0500)