I use a Bluetooth plug-in in my car that allows USB chargers to plug into it to charge devices. About a week ago it started turning on and off on its own, and I figured it was probably time for a new one since I’ve had it for a few years. Bought a new one, still doing the same thing. After a lot of trial and error I found that it works perfectly fine if there is nothing plugged into the USB ports. Same thing happens with a normal plug adapter. I need to be able to charge my phone in my car at times and I’m just trying to figure out a solution.
It seems there is a faulty connection to the 12 volt socket. if so you will need to get access to the rear side of the socket to check the connections to it.