It sounds like the IO board may be failing. Check out [guide|17049|this guide|new_window=true] for instructions on how to replace it. If you think the adaptor you're using could be faulty, then I'd recommend trying to borrow a separate adaptor for testing, or taking the device into a repair store for testing. It might also be a good idea to inspect the interior of the device for other signs of damage—something like this could technically be caused by a fault on the main logic board as well. Good luck!