Gaming possible on a Optiplex 790 DT?

Just bought a refurbished Optiplex 790 DT for a great price and would like to see if I could turn it into a low end gaming rig.. Specs are:

i7-2600

4GB Ram

250GB Hard drive

Geforce 210

250W PSU – 17.8 on the 12V rail

I am interested story type games and don’t really get into many shooters. First game up, Alan Wake. From what I have researched so far it will not run well with my video card, nor the cards on the Dell ‘valid’ list:

1GB AMD RADEON HD 6450, 512MB AMD RADEON HD 6350

But it looks like it will run well with this:

http://www.amazon.com/EVGA-GeForce-Profile-Graphics-02G-P3-3733-KR/dp/B00L5GZG5C

Problem is it recommends a bit more than what my 790 has to offer. I hear Dell rates things conservatively, do I have a good shot at running this card?

Or… Is updating the PSU possible? The Power Supply is a small version of ATX, right? So all I would have to do is find something with the same or smaller dimensions(like TFX standard) and has at least the same or more connectors (like ATX 24 pin, 12V 4pin..etc). Something like these guys:

http://www.seasonicusa.com/tfx.htm

If I would have to modify the case to secure the PSU in place so be it…. Am I missing something that wouldn’t make this possible? Thanks in advance for any opinions or suggestions…