FYI electric language. US and Canada uses 120/240 voltage systems. Campgrounds use 50 amp 120/240 volt systems. 30 amp 120 volt systems and 20 amp 120 volt systems. 115 volt and 15 amp (language) systems went away long ago. You seem to have two threads going so you will need to read both.
As for adaptors there are many. The first # designates from and the second # designates to. 50/30. That is 50 amp 240 plug to 30 amp 120 volt plug. Only one leg of the 50 amps is applied to the 30 amp cord.
30/50 is just the reverse of that. 30 amp 120 is applied to both 50 amp legs to the RV 50 amp main breaker. Only 30 amps 120 volts is available. Go over 30 amps and the Ped breaker will trip.