A power supply device of a video display apparatus and a method thereof is capable of improving operation reliability of a video display apparatus, preventing erratic operation of the video display apparatus caused by higher harmonics and preventing erratic operation of other apparatus caused by unnecessary transmitted radiative wave. The power supply device can include a rectifying section for converting AC power into DC power, a harmonic suppressor for cutting off higher harmonics included in the DC power and a smoothing circuit for smoothing the higher harmonics cut-off DC power. A standby power supplier is for supplying the smoothed DC power to the video display apparatus as standby power, a main power supplier is for supplying the smoothed DC power to the video display apparatus as main power and a control unit is for controlling an operation of the harmonic suppressor.