Systems and methods are disclosed for maximizing the efficiency of a power supply according to the value of a load to be powered. One embodiment provides a power supply system including a first and second stage. The first stage has at least one AC to DC conversion section for converting an AC input to DC at an upper DC voltage value. The second stage has at least one DC to DC regulation section for converting at least a portion of the DC at the upper DC voltage value to DC at a lower DC voltage value and supplying the lower DC voltage value to a DC output. One or both of the first and second stages includes more than one section operating in parallel. A controller selectively enables a selected combination of the AC to DC conversion sections and the DC to DC regulation sections according to an expected or actual value of the load.