DC power supply device and its method for adjusting output power

The invention relates to a dc power unit with correction ability for power factor, which comprises: an ac power, a rectification circuit, a filter capacitor connected to dc output port of rectification circuit, a reactor connected between ac and ac input port of rectification circuit, a short-circuit circuit to force conducting the reactor, a zero-crossing detection sector, a grid-drive sector, a Vdc detection sector with a potential-divider network, a sine-wave reference signal generator, a triangular-wave oscillator, a comparing element, and a control chip. This invention can increases power factor and reduces higher harmonic.