I was putting together a fairly basic LBB at the weekend to control a handful of DC devices which got me thinking. Why are both pin-positive and pin-negative DC barrel connectors used? Are there any *concrete, electrical* advantages to either design? Or is it just for manufacturer lock-in?

Pin-positive seems to me to be the obvious one to use from a safety point of view, but a quick audit of the supplies in my spares box revealed a not insignificant number of pin-negative supplies.