This is going to be something on the Amiga side pulling too much current for the connector to handle. The wattage of the power supply is not going to affect that- that only affects "how much" the computer can pull from the PSU.
The computer will pull this amount from a 250W or a 500W power supply- the only difference is if it pulls more than the rated amount, the protection will trip.
I guess you can lower the wattage of the power supply to something that will trip before it burns the connector. The connector may only be rated to something much lower... the original power supply is only <=150W.
