I want to upgrade my old graphics card but I don't want to have to swap out the PSU for something more powerful. Anyway, I'm not sure whether to get a GTX560ti (MSI TWIN FROZR II) or a GTX480 (with a zalman VF3000 cooler) and theres also the issue of whether or not i'll have enough juice to power either card. They both cost £140, so price isn't really a decider. My power supply is a Coolermaster GX-550W (it has 2 PCI power connectors). I know people say that the 480 is a faster card but it seems a bit outdated for a upgrade - I would really appreciate some help with this, thanks.
For gtx 480 Nvidia recommends 600w psu with 42A on the 12v rails, since your psu has 44A on 12 rail, it may work depending on the rest of the system. But there wont be any room for overclocking or extra fans/Hdd.
I reckon you should get the gtx 560 ti just to be safe. The msi version is good, you can overclock it quite a bit. gtx 480 isnt worh for the extra heat and noise.
You'll be fine. That is one of the decent Coolermaster psus and though the 480 is a beast, it doesn't draw anywhere near 550w no matter what cpu you have. Don't plan to add a second one.
Lots of people interested in the 480 now, because they are cheap right now and a lot of bang for the buck. The basic architecture is only 1 gen back (Fermi). I think its probably a just a great deal, but if you wait even a few months nVidia is likely to have their new generation lower end cards that will run a lot more efficiently and be a little more future proof.
I have to agree used PC parts are a minefield, I have done it once and was lucky. I would not spend £140 on a second hand card though. The 560Ti is not that far behind performance wise, depending on which one you get, and can be had new for around the same price.