GPU power usage?

Okay thats easy as, just go to the manufacturers website and find your model card, then look under specifications and it should have minimum wattage power supply you can use with the card and also the average power consumption under load.
 
You can find many sites by googleling GTX 650 Ti power consumption for example. Read the test setups carefully since 90% of the sites out there like to overclock the system to the max so it varies on setup.