Seems like it actually has 3 into one so should be plenty of power to run those cards.
From the jonnyguru review
This puppy sure has capacity on the 12V side of things, doesn't it? Almost the full output of the unit is available over there. And like I said, that whole 52A number goes to one, not three, 12V rails. 5VSB is a little on the high side, as not too many rigs would need 3A there, but it's cool to see all the same.