I have a Optiplex 390 and I need to upgrade the videocard. I am visually handicapped and need this upgrade to run some special software correctly. Someone has recommended the

GeForce GTX 650 Ti 2GB GDDR5 PCI Express. I am a little nervous about getting into the guts of this machine but I noticed that it required 400 watts. Looking at the online manual it says this unit only has 25 watts..Am I missing something. I think this card should just plug in.

I am a bit of a newbie to the upgrading world but not to computers. Any help would be just super :)