Power supply choice [Easy question]?

Well not always the wattage matters you could have 1000watts on a power supply and a crappy name brand which really only has 400watts so go for the more famous name brands like ATX and get a 500-600watt one i would say go with the 600watt so it wont give you trouble and it could work and if you get a more powerful GPU latter. The Higher the better. Good Luck