Rescued from the skip for some young friends. This PSU would typically be used to supply 5V for TTL logic, and +/-12V for RS232. Or even +/-15V for analogue circuits. It is an old, analogue PSU so it is very heavy. 

The components most prone to aging are electrolytic capacitors. They have a liquid electrolyte that slowly dries up. These are the first things to check or replace when servicing old equipment.

I notice that all of these old power supplies on eBay that are switched on to show they work, display a positive current without any load. This could be coincidence, or more likely they all develop this same fault with age.

It is a metering error, not a safety fault, so I'm happy to use it.

eBay prices vary from £125 to £250. So that saves a bit of pocket money.