Well I havea Carver M2040i (40x2/80x1watts RMS, true wattage here folks

) running crappy surround speakers off a 250watt PS (8amps @ 12v)
Now it runs the surround speakers fine, but they give off almost no bass.......so it's okay.
But when I hook up my 10inch Orion XTR car sub, which will strain the amp hard even in my car, when I hook it up to the PS the power LED on the amp severely dims with each bass hit (note that the volume is cranked), and after 5minutes the PS usually shuts down.
What model is your "500watt" amp?