Sigma Line® AUTOTRANSFORMER Application Notes for 125 or 250 Volt, 50/ 60 Hertz Applications
The autotransformers are frequently used to convert local Power line Voltage to some other Voltage value needed for a particular piece of equipment. Most often, this conversion is from 125 Volts to 250 Volts, or 250 Volts to 125 Volts. Autotransformers may also be used in voltage reduction type, lighting energy saving units (economy models), it may also be used as soft-starters for squirrel-cage induction motors.
Unlike an Isolation transformer, autotransformers use common windings and offer no interference or disturbance isolation, it would obviously a low cost option for voltage ratio conversion . You add any Suppression or Filtering networks your system requires.