What is an auto-select input in a power supply?

A 1-phase power supply with an auto-select or auto-range input detects the input voltage and automatically selects the correct input voltage range.

The choice is normally between the two nominal voltage ranges of AC 100–120 V and AC 200–240 V. The range in the device is switched using a relay or a thyristor. Stable operation cannot be guaranteed in the interim range. However, faults in the device are eliminated.

The majority of PULS power supplies have a wide-range input and not an auto-select input.