The right power supply for my PC

Hi, I just upgraded my video card to a GeForce 7600 GT 256 MB. It requires a minimum PSU of 350 W; the one I have right now is 305 W. As I want to avoid crashes (and since I'll be buying an extra gig of RAM), I need to get a new one. I'm looking at 400 W at the least, since that'll keep me on the safe side for power requirements. However, there are a lot of things about a PSU I don't know about. For example, I look at the options on Newegg and there are a lot of options for specifying what PSU you want. I can't make sense of it. Can anyone help me on what options to pick?

For example, for main connector, they list 20-pin, 20+4-pin, and 24-pin. I don't know which one to get or which one will fit my PC (it's a Dell Dimension E510). Other options are SLI support, Dual +12 Support, PFC (Active or Inactive), and modular cablin support. I really have no idea what to get, so can anyone help me pick the best PSU for my PC?

Jam it back in, in the dark.