How Does a Transformer Work? Figure shows a power supply unit found in school laboratories. It is connected to the mains supply which supplies it with an input voltage of 240 V. Using the voltage selector, you can select output voltages from 2 V to 12 V. What changes the input voltage from 240 V to a lower output voltage? The main component found inside the power supply unit … [Read more...] about How Does a Transformer Work?