What is the principle of a voltage stabilizer?

A voltage stabilizer is an electrical appliance used to feed constant voltage current to electrical gadgets like ACs and computers, and protects them from damage due to voltage fluctuations. It works on the principle of a transformer, where the input current is connected to primary windings and output is received from secondary windings. When there is a drop in incoming voltage, it activates electromagnetic relays which add to more number of turns in the secondary winding, thus giving higher voltage which compensates for loss in output voltage. When there is rise in the incoming voltage, the reverse happens, and, thus, the voltage at the output side remains almost unchanged.