the easiest way is to use a shunt resistor and measure the voltage across it, and for AC you could use a current transformer. But the advent of the Hall-effect sensor has provided us a much better ...

While troubleshooting the power supply of a 1970s Centurion system, [Usagi Electrics] came across a fascinating feature of these units: the ferroresonant, or constant voltage transformer (CVT).

before electrical power leaves a power station – it is transferred at high voltages ... work with an alternating current (ac) input. This transformer steps up the voltage by reducing the current.