This paper proposes an on/off control of boost power factor correction (PFC) converters to improve the light-load efficiency in paralleled power supply units (PSUs) for servers. The proposed scheme operates the PFC stages of two paralleled PSUs alternately during one cycle of a 60-Hz ac input only at light loads. This improves the light-load efficiency without deteriorating the heavy-load efficiency by reducing load-independent losses such as capacitive turn-on and core losses. In addition, the proposed scheme alleviates the harmonic distortion by reducing the discontinuous conduction mode region. Experimental results from 1.6-kW PFC boost converters are shown to verify the proposed work.