Adapter randomly preventing motorhome from starting

I was having a problem where my motorhome would not crank over or would crank over and not start. I took it to Freightliner to get the problem diagnosed. They unplugged the adapter so they could plug in their computer. They found no problems and it cranked 40 times straight. So, after spending $245, it was determined that the adapter was the problem since it would crank every time with it removed. Has my adapter gone bad or does it need upgrading? I am currently on a long trip, so if I send it in I don't know how you could get it back to me since I am moving.