The GTX 680 has TDP of 195W. So you need a PSU that has two
6-pin PCIe power connectors and a minimum
of 17 amps current rating on the +12V rail.
The XFX 550W
is fine. If you live in Canada, you can select it via the dropdown at the top right corner of the site. If you live in Australia, then I'd recommend the Antec High Current Gamer 520W