PSU to fit my stock case and power a GPU

Fridder

Honorable
Jan 12, 2013
7
0
10,520
I have a stock computer (Gateway DX4860-UB33P) that I bought back in 2011. I didn't build my own PC (and I regret it). I have a stock Lite-On PSU, and the case only permits a very certain size PSU. Anything bigger would not fit whatsoever. The PSU's model number is PS-6301-08A. It's dimensions are 5.5" x 6.0" x 3.35"~3.4"ish. Here's a picture to sort out any possible confusion:

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(ignore the PSU model, the numbers are correctly edited)

I'm going to buy an EVGA GeForce GTX660 superclocked from Newegg, so I also need a PSU that can power that GPU properly (and of course my computer). EVGA recommended an EVGA NEX750 PSU when I emailed them about a PSU that can power the GPU with the proper amount of 'whatever amps' on the 'whatever rail' (I'm still learning about PSUs). This doesn't even come close to fitting inside the tower. The only PSU that fits inside of my tower that I found was an Antec TP-650C. Would this be able to power the GPU that I listed above? And what does "24 amps on the 2v rail" exactly mean, and where do I look for those numbers when shopping for a PSU?

tl;dr what would fit my case and power a minimum of 450w (and 24amps on the 2v rail) with 5.5" x 6.0" x 3.35"/3.4"?