12 volts & it Blows up!!

Hi Fellow caravaners & please excuse me if i appear dense with this thread, but I'm still a newbie to world of caravaning; We have a 2010 Lunar Quasar from new, never really used the 12volt plugs until last week. I plugged my 12 volt car charger for my iphone in, it started to smoke & blew up. Stupidly following day I plugged in the DVD screens from the car (forgot the 240 leads) same thing happened blew the unit up, now really unhappy just bought them from Halfords (though they have replaced them).

 A helpful caravaner on neighbouring pitch tested tested the 12volts with a volt meter, there pulling about 13.5 v, and there doesnt seem to be a fault with electrics .Now am I missing something hear, shouldnt these in car things work in the caravan? Any advice gratefully recieved appreciated