All the parts of the assembly are directly orderable in digikey, ebay, amazon or aliexpress except the meter circuit.I made a custom meter circuit shield for Arduino able to measure up to 36V - 4A, with a resolution of 10m V - 1m A that can be used for other projects also.The mains voltage comes in through an IEC panel connector (10) that has a built in fussible holder, there is a power switch in the front panel (11) that breaks the circuit formed from the IEC connector to the transformer (9). The 21 VAC go directly to the power supply circuit (8).
The AC input is also used to generate a negative biasing voltage to reach 0V.
There is no thermal protection in this circuit, so appropriate dimensioning of the heatsink is very important.
These potentiometers do not need to be multiturn, I have used the original potentiometers from the power supply circuit.
The 20x4 I2C alphanumeric LCD (1) is wired to the meter circuit.
There are two potentiometers wired to the meter circuit (2).