Defective or miswired adapter come to mind although your rig could also be miswired.
I have a 30/50 amp adapter that I've used for years on other MH's. Tried to use it on the Magna and the electrical protection built in wouldn't "approve" the power. Changed to a different adapter and everything is fine again.
2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft
Charter Good Sam Lifetime Member, FMCA, SKP
RV'ing since 1957, NRA Benefactor Life, towing '05 Odyssey