I wasn't sure where to put this. It's not old hardware, and not anything that fits in any of the specific threads, but I'll try here. I have a relay board that is able to control relays with MIDI-signals. I was going to use this using sysex commands from MS-DOS. It can run on 9V AC or 12V DC. 9V AC is required for this board when using dimmers, which my version does not have. I was going to use 12V DC. My question is, when looking through the documentation provided online, I can't figure out what is positive and what is negative on the power input. The documentation is located here: https://www.robot-electronics.co.uk/htm/midi-rly8.htm

Anyone help would be appreciated.