That's not opinion, that's fact. That's why the breaker size in the rig is 20A. I am puzzled why, especially with an extension cord (?? wire size and length unknown) in the mix, how the A/C would have started at all.
I'm betting that the extension cord is now "deceased" and the A/C and RV will be fine when plugged into a proper source without adapters and cords.
Nope, plugged right into a 30 amp box while camping for the 4th of July. Still had same affect. Had my brother over here today with his trailer. Used same extension cord and same garage outlet. His worked just fine. It is something wrong with the AC unit itself.