2 GPS adapters have been blown. First one was just the fuse. I bought a new GPS (it was just time) and I have changed the fuse. Even though the first one looked fine. I tried the 2nd GPS adapter, and it cooked that one too. Badly. I had not known that the cigarette lighter was the culprit on the FIRST GPS adapter until now.

It overheated the 2nd one to the point where smoke came out. The cigarette lighter fuse is ok. What do I check next?

 

I would double check to make sure the correct fuse is in place. If the wrong fuse is in place, it's possible that something could go awry. If you have a voltometer (or a friend that has one) check to see how much power is going through to the lighter. If its getting too much power, there could also be a wire crossed somewhere if someone did a poor wiring job on a previous repair. Many cigarette lighters (at least in other non-volvo vehicles i've worked on) also have an "in-line" fuse just before the wire cigarette lighter connects. Check to see if there is a second fuse too.

Hopefully some of this might help you check these off your list to solve the problem.