Hi, i've had my Dell Xps 8500 for nearly 5 months now, i've been playing games at low settings with my GT620. I was wondering if it would be possible for me to upgrade to a GTX 650ti or a GTX660 without replacing the 460 Watt PSU?
You should be able to upgrade to either one without upgrading your power supply. The GTX 650 Ti will take one 6-pin power connection and the GTX 660 will take two. You have two available on your power supply. Both are big improvements over the GT 620.