A short-circuit sense circuit and a power supply according to an exemplary embodiment of the present invention use an auxiliary voltage, which is a both-end voltage of an auxiliary coil coupled with a predetermined turn ratio to a secondary side coil coupled to an output voltage. After termination of a start-up period, the short-circuit sense circuit samples a sense voltage, which is a voltage of a node between a first sense resistor and a second sense resistor coupled in series to both ends of the auxiliary coils and determines whether a short-circuit occurs according to a short-circuit sense signal that depends on a result of comparison between the sampled voltage and a predetermined reference voltage.