The fast data center growth and cloud computing implementations drive the demands for a higher server system power efficiency to reduce data center energy cost. In this article, a novel control strategy is explored for power optimization to key components in a server system, using the voltage regulator (VR) control as an illustrative example. The new approach is based on the unique active disturbance rejection control (ADRC) principle, which actively estimates, and compensates for, disturbances to the system caused by dynamic load changes rather than passively reacting to them as most existing methods do. Hence the controller is inherently efficient in rejecting the disturbances in real time. Without any hardware changes, this methodology leads to substantial power saving in a highly dynamic load environment in a simulation study.