If you plan to have 2 GPUs in the end its a safe bet to go with a 750W PSU if your going just for a single GPU than a 550W PSU should do the trick but without know the specs of your build thats the best advice I can give right now.
If you plan to have 2 GPUs in the end its a safe bet to go with a 750W PSU if your going just for a single GPU than a 550W PSU should do the trick but without know the specs of your build thats the best advice I can give right now.