This is a replacement PSU for the Commodore C64. The original PSUs from the 1980s and early 1990s tend to die and damage the connected C64, so it is recommended to get a new power supply for the C64. This design is straight forward: a transformer, bridge rectifier and DC/DC converter for the 5VDC and a separat winding for the 9VAC. Nothing fancy. It was paid attention to use parts which are easily available (in Germany). Everything, except the 4 conductor cable for the output voltage are sourced from reichelt.de. A further goal was a decent documentation.
Find some info on the required cable making on my website