Initially, I was planning to replace the P-ADB connector of my AppleJack controller with an ADB plug (Mini-DIN-4). The remaining P-ADB plug attached to a Mini-DIN-4 socket would then become an ADB adapter dongle.
But why would I destroy the cable of my only controller? According to the documentation, which can be found here and here (in a very low resolution, unfortunately), a “Hosiden HGC0492-01-010 or equivalent” connector is needed. And that connector is impossible to find.

To get started, I created a new schematic based on the available documentation: