It’s a classical +5V/+12V PSU used to power PC peripherals. The most faulty-prone part in this PSU is TDA4605 controller. The PSU has an additional “Standby” input wire. When this wire is floating, the PSU will remain shut down. Applying +5V to this wire will make the PSU start and generate output voltages.
Hard Disk Drive
The hard drive used is 20MB Seagate ST325-X (other spec). The drive in my HD20 had different jumpers than the ones described in the specs. It had a section of 3 jumpers, which meaning is not known to me. As I received the drive, it had the middle jumper installed. With this jumper the computer refused to initialise the drive and boot from it. Only when I removed all the jumpers, it started working correctly.
Here are the screenshots of some of the programs I found on the HD20.