The VIC20 PSU is a small PSU for connecting to a VIC20 CR (Cost Reduced that has a DIN connector instead of the 2 prong on the older VIC 20)
Input is USB Type-C PD from a 15W USB power supply.
It generates 5V to the logic and 9V to the Datasette cassette interface (motor driver). The 9V is normally AC, but in this case we can get away with DC which simplifies the design a alot.
What doesn't work is the 9V AC normally found on the User Port. This was historically used for Modems, RS232 interfaces and EPROM burners for boosting to a higher voltage and/or inverted voltage. These peripherals are extremely seldom used today, so I think it is a balanced approach to give that up for a more robust, low cost system that draws power from a modern USB Type-C source.
