and cell phones?
The safest thing to do, which will add more wires, is to power everything off a little inverter.
What happens with modern vehicles is the electronics you have plugged into a DC outlet can talk to the vehicle in some instances. To eliminate this the power inverter seperates the electrical signals so there is no cross talk.
When I say, talk to, I mean the devices put off signals, electrical surges, static, whatever, and the vehicle CPU might read this as a sensor on the vehicle and then do something odd like make minor engine adjustments.
