I've spent probably around the last 2 hours looking up info on PSU's and have yet to find any answer to this.
Based on the image in the above link, can this PSU run an EVGA GeForce GTX 660 SC or is it worth just upgrading and if so, is the Corsair TX650v2 better than this, if you can tell from the image? This is the stock PSU for my HP Workstation XW8200 and this photo I've taken is as much info I can find about the PSU anywhere. The biggest problem I have is the +12v rail stuff. From what I can tell from all the reading I did this has 3 rails and an extra 2 for the CPU's? Or by "minimum amps on the +12v rail" from here (http://www.evga.com/products/pdf/02G-P4-2662.pdf) does it mean the "Max. combined current on +12v" it says on the PSU? I'm really stumped at this and it's just frustrating me so much.
Sorry if this doesn't make much sense, reading about PSU's for 2 hours has fried my brain.
You can add up the 12v rail ratings if your power supply has more than one. Your video card will list a minimum wattage requirement which can include the rest of your system if you don't have too many drives running off the ps. If your evga is the 650w model and has 4 20 amp rails, it should be more than adequate even for overclocking as long as you use just one video card. If you go with two for sli, then you may need more juice.
ick...i don't like that PSU you have. Typically, older prebuilt PCs don't have PSUs capable of running higher end graphics cards. It says "max combined current on +12V = 43A", but each individual rail is less than 11.4A, and two of them are for the CPU only. i just don't like it. you don't want to ruin the rest of your rig by using a bad PSU. on the plus side, you can get a relatively inexpensive power supply because the GTX 660 doesn't use THAT much power. you could easily get by with this PSU...
BTW, the correct way to determine the max number of Amps on the 12V rails is this...
max watts(which is Volts x Amps) on 12V rails/12 Volts. For example, the max number of watts that can be used by the 12V rails on the power supply i suggested is 350W, so you take 350W divided by 12V and you get 29.2A max across the two rails. It is NOT 18A+18A = 36A.