I am not sure how it works on the amiga, but it was a common trick in the PC world to leach power off the DTR and RTS lines which idle at +12v and can provide a

I am not sure how it works on the amiga, but it was a common trick in the PC world to leach power off the DTR and RTS lines which idle at +12v and can provide a few ma of current per the RS-232 specs. This is also why a lot of peripherals will fail when you use a knockoff 'rs-232' adapter that only outputs +-5v instead of +-12v