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Hi my name is Robert...
Are you using any adapters or extension cords on the main cord?
Do you happen to have a generator built in?
The power should go right from the cord outside into the main breaker panel inside. Sometimes adapters can cause issues, I would advise if at all possible to plug in without any adapters and see if the problem goes away. IF you have not tried another supply post I would try another and make sure the post does not have a tripped breaker.
Beyond that you would have to see if AC power is getting to the breaker panel inside if AC power is not getting to the main breaker then it could be a connection issue at the breaker panel or issue with the shore cord. Robert