Power Supply Unit (PSU)
From Night Vision Wiki
The PSU (Power-supply-unit) converts lowvoltage (commonly between 2 and 12V, depending on the unit) into the , for the tube needed, highvoltage (up to 60kV for cascade designs). Most PSUs are a 2 stage design with a lower voltage part (often 2kv) with all the control logic in 1 stage and the highvoltage stage which creates the highvoltage for the Phosphor_Screen. With older designs often each stage is a seperate component.
The logic inside the 1st stage is responsible for functions like Automatic brightness control, Bright Source protection or Autogating.