Did you already buy that PSU? I hope not... The NEX series is rather low quality.
A company called CableMod can hook you up, their website is
http://www.cablemod.com and it's very easy to navigate. Simply hit Store on the menu, choose your location, and then click Configurator on the menu (menu will change once you enter the store).
A good quality PSU for the wattage you need would be the Corsair RM650x.
http://pcpartpicker.com/product/Rp8H99/corsair-power-supply-cp9020091na
CableMod produces cable sets for both the SuperNova NEX and the RM650x.