It's easy to find out your ratings. The ratings should be on the side, top, or bottom of your Power supply, a big sticker with the info on it. All PSU have that big sticker on the side with the ratings.
Here's a pic
What is your amps on the 12V Rail?
1st pic: +12V@16A
A minimum PSU should have a minimum of +12V@18A and a 16ms hold-time
If you are getting a PSU for a system with a single high end video card than 28A-32A should give plenty of room
Midrange systems should shoot for 24A on the 12V rail
Really low-end, older or specialty systems can consider 18A on the 12V rail