Hey,
That depends on the rest of your system. What are the specifications of your machine?
Also what brand and model of power supply is it?
If your components don't use too much power, and providing that its a quality PSU with one 6pin pcie connecter, then yes you can power a gtx650. A gtx650 requires a 400watt psu, as it does not draw a lot of power.
Hope this helps!