What happens if you plug a 50 Amp RV into 22V welder plug

Since I was not there to see what he actually did I cannot say exactly what happened. However my friend in another state who works in home construction supply business wired up his own 50 amp RV recepticle and when he plugged his brand new Class A motor coach in it blew up the converter, all the appliances including the TV and other items. $$$$$$$$$$$$$ Be sure what you have before plugging in. The pictures in the above posts are very good!!!