Will my power supply handle it?

I actually have no idea what brand PSU I have, it came with my premade cyberpower, which I bought when I knew nothing about computers and thought it was actually good. I upgraded my ram and GPU, but later I found my cpu and motherboard was lacking.

My motherboard is ASUS M2N SLI NVIDIA nForce 560 SLI Chipset, which I'm fairly certain can't CPUs without a am2+ socket.

A fast check and it looks like you might be good with the Athlon II and Phenom II CPUs.
I was looking at http://www.cpu-upgrade.com/mb-ASUS/M2N-SLI.html
and thinking about the $78 Athlon II X3 445 Rana 3.1GHz triple core.
I think 3 cores at 3.1Ghz (before overclocking) is probably a better option, in most cases, than 4 cores @ 2.5Ghz.

And the Asus Support site confirms it.
ASUS M2N SLI CPU support list with BIOS 5001 or later.

Hmm, well according to PassMark, the triple core got a 2881 score and ranked 140, while the quad core has a 2963 score and is ranked 134.

Here are some real world benchmarks that show you where the X3 440 is better and where the X4 9850 is ahead.
The options didn't include the X3 445 which would be a little better.

Well I guess I'll stick with the X3 445 then. My PSU will definitely be able to handle it?

I don't expect your PSU to have any problem since it's been running that OC'd video card and OC'd x2 5200+.
Just to be on the safe side I'd roll the GPU back to stock clocks for the initial install and testing period.

The X3 445 is overclock friendly too. The X4 9850 barely reached 3Ghz and the X3 445 was nearing 4Ghz for some people.
AMD Athlon II X3 445 3.1GHz Triple Core Processor Review
AMD Phenom X4 9850 Processor Review

Glad to know I won't be needing to spent another 70$+. Thanks for the help.

Be sure to let us know how it works out for you.

I won't be buying it for a little while at least, gotta finish paying off Final Fantasy XIV first, heh.

Best answer selected by Frybrain.