Differential power processing (DPP) has been proved effective in many applications. This paper presents a Series Voltage Compensator (SVC) with partial power processing to compensate for the voltage difference between a variable dc bus voltage and a regulated load voltage required by the DPP system. The SVC is connected in series between the variable dc bus and the DPP system. It regulates the input voltage while only processing a fraction of the overall power. A variety of SVC topologies are compared and their performance limits are studied, providing insights into the power rating design and regulation range selection of SVC topologies. To validate the principles of the SVC, a buck-derived SVC is designed and applied to a 10-port MAC-DPP converter. The buck-derived SVC can efficiently convert an input voltage ranging from 50 V to 85 V into a regulated 50 V and feed it to the DPP system. It achieved 98.8% peak system efficiency while converting 55 V into 50 V.