I would add another possible explanation: The plug for that seat's onboard power is potentially worn or deformed and not successfully closing the current loop.

Whether on purpose or not, I've found many plugs to be non-op because of what previous users have tried to or have plugged in, only to make the socket not even work with small AC-to-USB plug-ins.

Adding to that, others have brutalized some of the newer AC+USB plugs so that the USB sockets aren't working.

David