Anyone who develops circuits using microcontrollers knows that plug-in ‘wall wart’ power packs do not always make suitable power supplies. On the other hand, a proper laboratory power supply is expensive overkill — it’s too bulky and generally delivers only a single voltage. The PSU described here is small and supplies controllers with the 3.3 V or 5 V used typically. A second preset voltage between 0 and 15 V is provided for peripherals.