A system with a GTX 650 Ti needs a recommended 430w power supply. That's for the entire system not just the card. http://www.realhardtechx.com/index_archivos/Page362.htm
Manufacturers do not just make up a number when they recommend a power supply wattage. They have to assume you have a generic, low quality unit and base their recommendations on that.
The GPU is the main power hog in any modern system. Fans use a few watts each as do hard drives. With no GPU pretty much any computer woud be fine with a 250w power supply.