Hmm, they sure sound different from what I've got
here; are they made
by Digital Products Inc.? Any idea when?
The front panel has clearly printed on it 'Digital Products Inc, The
SubLAN(TM) Company'. I have no obvious idea as to the date (I would guess
early 80's), but I can extract it from the pile _sometime_ and read the
date codes on the chips.
These units all have internal power supplies.
Most of the PSU on these ones is internal. There's a <mumble> pin DIN
socket on the back that takes in a couple of low-voltage AC supplies from
an external transformer. The rectifiers, smoothing capacitors and
regulators are on the main PCB.
FWIW, access to the configuration menu is ~~M, but you get a full screen
menu, not just a prompt.
It's a long time since I did this, it might well be the same on this unit...