Yes, the GTX 650 Ti would be a better card to get.
Not all power supplies are created equal. If you upgrade your power supply, make sure it's from one of these manufacturers: Antec, Seasonic, Corsair, PC Power and Cooling, FSP (Fortran Source). Buying and installing a cheap/no-name power supply puts your entire system at risk or electrical damage.
PCI-E is the graphic card standard
PCI-Ex16 is the physical graphic card slot size and bandwidth standard
PCI-E 3.0 is the version of the PCI-E standard and it's actually PCI-Ex16 3.0
Yes, you can use that card.