I'm fairly sure the radio only runs 100 watts.  Also, if it were the power 
supply, usually they just shut down if you pull too much current.  One way 
to tell is stick a volt meter on it with and without a carrier and see if 
it drops.  As I said before, power supply problems don;'t sound at all 
like rf feed back.  You either would get hum or in severe cases, the 
signal would fm on peaks.
73s
Butch Bussen
wa0vjr