Anyone ever seen one of these before?

(Unable to reply to this message for reasons unknown to me, I've used my moderator powers and edited in a reply instead)

Yep. There's one in every Beocord 6000, 8000, 8002, 8004, 9000 and it's not external, its a plug-in module.
This one is a 120V 60Hz version so would be fine for a US-conversion of a european machine.

Martin