What is the affect of having a lower wattage power supply?

The effect will be that the PSU will go into some kind of protection mode at a lower delivered output power into the load.

The amp doesn't give many (any!) clues to its real power output i.e. is it watts rms or some other measure such as total peak music power?

500 watts rms (per channel) is a huge amount and I can't see that module coming anywhere near that. Neither supply would allow that anyway.
 
  • Like
Reactions: Lawnboy