It's possible for sure, depending on the rest of your system. What would concern me is that if you have enough money to spend on two GTX690s then it's quite likely you have a high end motherboard with perhaps a heavily overclocked CPU which is going to be eating power too.
Given you are talking about $2000 worth of graphics cards, I'd be inclined to get say a 1000W+ as it's going to be a fraction of your total cost.