ADL-1 OTP Printers shipped prior to 2018-11-15 operating from external power in excess of 13.8 volts dc will cause the voltage regulator to overheat and malfunction. This causes the printer to be supplied with excessive voltage and will cause the print head to melt and burn the paper.
Do not operate the printer using external voltage in excess of 13.8 volts dc. Operating the printer from the batteries bypasses the voltage regulator and works just fine.
So, don’t run it over a standard power supply output. I just use batteries in mine.