This is the Cambridge Co-Processor complete with Acorn moulded plug. The adapter is Acorn badged which is quite unusual for a cheese wedge as they tend to be BBC badged. I wonder if this edition was intended for the Acorn Cambridge Workstation and the 32016 badged version for the BBC micro.

Another significant feature of this unit is the term "co-processor". Initially all the Tubes were known as Second Processors but by the time the Master Series came out, the internal expansions were known as co-processors. This one must have been issued some time in between the two.

Picture courtesy of Matthew Cook.