The PSU-12 is a small utility power supply module that generates a 3rd-power rail (typically +5V or +6V) as sometimes required by some older 4U designs.

The +12V/0V/0V/-12V input to a 4U boat is terminated to the left-most connectors on the PSU-12 while the +12V/+6V/0V/-12V connectors to the right are used to feed the boat.

The PSU-12 has an adjustable output over the range of ~4.5V to ~7V and can deliver up to 1A.