With the exception of the case, everything in this unit came from eBay sellers. It contains four separate power supplies. Each unit has its own transformer, its own voltage control circuitry and its own volt meter. The case also contains the circuitry to supply 15 volts AC to a CDU.
In common with the Block/Cab Controller this unit uses a module based on the LM317 variable voltage regulator. There are many versions of this module to be found on eBay and at a variety of prices.
The volt meters are also eBay units. If you wish to make a similar unit you should be aware that you will require to supply the meter with a five volt supply in addition to the voltage being monitored.
I have decided not to give full details regarding the wiring of this unit as I have no control over how it would be used and mains power can kill.