I received this in a box filled with primarily Atari stuff that I purchased at a garage sale. It doesn't appear to fit any of the Commodore systems I currently own.

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I was able to find this auction on eBay, which looks to be identical to the item I have, and identifies it as a Commodore Plus/4 power supply, but the images in the Commodore Plus/4 entry on Wikipedia depict a system with a circular power jack, and a significantly different power supply design.

Any ideas?