This paper proposes a new control method in the phase-shifted full-bridge converter for the server power supply, which is variable delay time of lagging-leg switches under the light load conditions. By widening the delay time, the switching occurs at the lower drain-source voltage and then switching loss can be reduced under the light load conditions. The voltage stress of synchronous rectifier switches is also reduced. Without additional power devices and side effects at heavy load condition, the higher efficiency under the light load conditions can be obtained. The analysis and experimental results are presented in this paper to confirm the validity of this study.