Power supply capable of protecting electric device circuit

A power supply comprising:

• a rectifying unit for rectifying an AC power into a first DC power and a second DC power and outputting the first and the second DC power;
• a main power supply transformer for boosting the first DC power and outputting the boosted first DC power to an output;
• a switching controlling unit driven by the second DC power, for performing an operation on said main power supply transformer which causes the first DC power to be boosted when the second DC power is received;
• a controlling unit for determining whether the second DC power is to be supplied to said switching controlling unit;
• an auxiliary power supply transformer for boosting the second DC power;
• and
• a photo-coupler for providing said switching controlling unit with the boosted second DC power based on an output signal of said controlling unit,
• wherein said controlling unit senses a voltage at the output, and interrupts supplying of the second DC power to the switching controlling unit if the sensed voltage exceeds a given value.