Its about how many amps you have on the rails, a good quality PSU can punch above its weight in the wattage stakes. but tbh I don't know the draw of that card though i'd be surprised if there is any single card setup that needs more than a HX620
Edit: your card has double the maximum draw of mine so you my want a bit more. the HX620 is 100W more than my PSU but your card can draw 150w more than mine (in something insanely intensive like furmark anyway).
http://www.behardware.com/articles/781-6/report-the-true-power-consumption-of-73-graphics-cards.html