To find out your PSU, you'l have to physically open your PC case.
The PSU is usually the Box at the top or bottom of your case with power cables coming out (the largest cables).
On there, there should be a company name and/or model number, usually printed on a sticker.
From that you can find out your exact PSU make, and usually the supported wattages and amperage on it's rails.
-good luck