My Power supply is 480w. I know it says I need min 500w but I used this site: http://extreme.outervision.com/PSUEngine
put my stuff in with the new card and it said: Minimum PSU Wattage: 347 W Recommended PSU Wattage: 397 W. Should i be good with what i have or do i really need to buy a new PSU. If so what would you recommend.
More about :buying radeon 7850 2gb 256 bit gddr5 power
7850 uses a 6-pin and the PCIe lane as power imputs, so that (if i recall correctly) sums up to a MAXIMUM power draw of 150+75 (6-pin + pci) so I'd say you are pretty much on the limit there. Remember that wattage is not that important, the important part is the Amps that the 12v rail (preferently, a single 12v rail, avoid multiple) can deliver. A good 480w power supply should be able to deliver about 420w efficiently, so try not to overdue it.
If you dont know anything about efficiency or actual power being delivered by your PSU, it may be a good idea to buy a new one, not for the watts, but for the reliability. Usually those OEM systems use really crappy power supplies.
Im not an expert though, wait for further comments c: