I don't buy it, literally and figuratively.
Something else is afoul, even a faulty DC adapter or a faulty GPS should not kick on the Check Engine light.
The DC socket only supplies 12Vdc power, it doesn't feed info into the OBDII/CANBus network. There is no send/receive data going on here.
If anything, if the GPS was faulty, it would blow the fuse.
As RoboCop would say,
"Step Away From The Vehicle, Final Warning !!"