Basically I ordered a dell xps 8700 (specs below) and after checking the order sheet I was surprised to find the psu not listed, I'm hoping to upgrade the Geforce GTX 645 (OEM) supplied to a Geforce GTX 770 or 780 and I don't want to have to upgrade my psu. So basically I have two questions what psu does the dell xps 8700 use and will it support any of the graphics cards I mentioned. (I don't intend to upgrade the psu unless the situation is dire because I can't afford a new psu and a new graphics card.)
Specs
CPU Intel 4th gen I7-4770 3.4ghz quad core 8m cache
GPU Geforce GTX 645 (OEM) 1gb
RAM 12gb DDR3 dual channel
2TB Sata 7200rpm 6gb/s
Specs
CPU Intel 4th gen I7-4770 3.4ghz quad core 8m cache
GPU Geforce GTX 645 (OEM) 1gb
RAM 12gb DDR3 dual channel
2TB Sata 7200rpm 6gb/s