These transformers work under magnetic saturation and resonating principals at the mains frequency.This is done by suitable leakage inductance and Ac capacitor. Saturation effect results in distortions and which is compensated with a series inductor to get sine wave within 5% distortions.The leakage inductance helps in current limiting in event of short circuit. The output voltage regulation is within 2% for input variation 70 to 120% voltage output 0 to 100% load. Because of current limit features not recommended for high inductive loads (Motors).The saturation of core results in higher no load losses hence poor efficiency at less than 25% load.Without capacitance which can work current limiting suitable for constant current mode.