Well first of all the GTX 560 TI needs one 12V rail at 30A. You didn't mention the manufacturer and model of your current power supply, so I can't say if it's a good or bad Power Supply.
GTX 560 Ti needs:
2 x PCI-e PSU Connectors
12V rail at minimum of 30A
I'd suggest a good 600W Power Supply. Like the Corsair GS600
It has a single 12V rail at 48A: $90 at Newegghttp://www.newegg.com/Product/Product.aspx?Item=N82E16817139023&Tpk=Corsair%20GS600