I looked up some info about the computer but unfortuantely I couldn't find any more details on the Power Supply besides that it's a 500W like you said. If you could open it up and look at a sticker or any labels on the power supply to see if it shows the brand name as well as the amps on the 12v rail(s). It would look something like this: "12v 30a"
But I'm guessing you will want to get a different one. Unless you got a special model or something the stock gpu in that PC is a GT 610, which takes like no power so they probably just put a no name crap 500w in there since it would be enough. I'd suggest getting a good quality 500-600W PSU from Antec, Seasonic, or Corsair.