Pretty sure it's a standard ATX PSU. According to PCmag
it's 460W and capable of powering a 225W graphics card, so a GTX 660 Ti or 670 should work without any issues. I don't know what number of PCIe connectors is supplied though. If only one, better go with a 7850 or 660.
Why don't you want to build it yourself?
I would look at other pre builts though. Digital Storm
, maybe. Also heard good about Maingear