An apparatus, method, and system for actively controlling power in a series string load is provided. A number of conventional low-cost power supply units energize a number of voltage-regulation modules (VRMs) connected to each other in series. Each VRM generates a regulated output voltage using a pulse-wave modulated switching circuit, and provides the regulated output voltage to a number of load elements. Each VRM also sends signals to a central controller describing the output voltage applied to its connected load elements, and adjusts the output voltage applied to its connected load elements in response to signals received from the central controller. The supply voltage provided to individual load elements may thus be accurately and dynamically controlled during operation. Each load element may comprise a light-emitting device, a microprocessor, or a cryptographic integrated circuit with a plurality of processing cores. Optocouplers or load-shifters send signals across different supply voltage domains.