Power Converter HELP

Ok so I have an old FEMA trailer that I bought for my deer lease. I have had it since 2013 and have always used power from the ranch. I have never had a battery on my camper. I went down to the ranch a couple of weeks ago, I pulled out the power cord, plugged it in, went inside and there was no power. I checked the power supply outside and had power so I went back inside to see if the breakers were tripped and they were not. I said well lets see if the microwave works, when I turned on the microwave the whole trailer fired up and I had power. Does this sound like a ground issue? Is the power converter like a alternator on a vehicle where it either works or it doesn't? This is the first time this has ever happened. Where is the ground wire is it mounted to the frame of the trailer? I had a lady from CCRV tell me I had to have a battery to run the trailer which I have NEVER had I have always plugged the trailer into the power supply at the ranch since 2013. Can someone please help me? Thanks Jeff