i'm using my brother's old 620w psu, wondering if it will be enough to run my new system.
Is it a gold psu or lower. I would recommend a 850w for 2 high end cards
660s aren't high-end cards, though. Efficiency isn't an issue, either - it's actual output OP needs to worry about.
First, how old is the power supply? Second, there should be a label on the side of the unit that looks like this; the important number is the amperage on the 12V rail(s), which is 35A in that example picture. Third, what's the make and model of the unit?
A photo of that label should take care of items 2 and 3 for us, if you can manage it.
the psu is at least two years old. i'm gonna have to wait until i get my hands on it to get the label