The Power Brick Connector for the APS Technologies Portable HDD case I got for the PB100's stock 20MB HDD back in the day has exactly that type of power connector. It just has the three top pins in your pic implemented, the bottom three are missing, but there is room for them.

I'd say it was more of a Mac KBD Converter for a KVM setup if that's the direction it works. Lack of V & M provision to/from the PC side makes me wonder though.