I had a very similar problem with all my electrics failing, we were on site and late at night everything went.
The following morning I checked and tested just about everything which could possibly cause this total power shutdown - all to no avail. I eventually unscrewed the front of the power unit in the wardrobe and pulled the unit out of the casing to find that the connector had completely come away from the socket, ( just like a kettle socket), I pushed it back in and were were sorted.
I can't think how this could have worked loose but could only think it wasn't plugged in properly when the caravan was new.
Hope this helps in some way.