can you see the exact model and manufacturer of your psu?

300W is quite low really. If its quality one, id say "maybe" (for the 750 TI) - but if some random manufacturer id consider changing it regardless what you do with gpu.

What kind of games youre planning on playing? 750 Ti is power efficient - btu its not really powerful. list some games yuoure interested in=?

This whole upgrade endeavor was actually caused by my attempts to play Wildstar. Which I don't think is a graphic intensive game, my current GT 620 just sucks.

In terms of high-end AAA gaming, I do most of that on xbox. I use my PC for MMOs, strategy games, GOGs and various PC exclusives.

A stock 750 Ti takes 11W more than a stock 620, according to NVIDIA's site. An overclocked 750 Ti (like the card in the link) might take 20W more than the 620. A 300W PSU will still happily run it, IMO.

For your purposes I think that even a plain GeForce 750 (not Ti) will do, such as this one. It's 10%-20% slower than a Ti, but it's cheaper and takes a little less power.

GOG ate my post :/(

I just checked some Wildstar threads like this: http://www.reddit.com/r/WildStar/comments/24jkfy/looking_to_potentially_upgrade_to_the_750ti_vs_r9/

And apparently 750 Ti is pretty good for that game atleast.

270X/270 or GTX 760 would be more powerful - but also more powerhungry. And bit more expensive on depending on model.

Id recommend anyone to have PSU of 400-500W these days. Quality 400-450W PSU is easily enough for any single GPU thesedays. however, if youre not interested in buying new PSU (400W Seasonic, Corsair, Silverstone forexample cost around 60usd, BRONZE) - then the 750 Ti is probably the right course to take now.