This paper presents a Modular Series-Parallel architecture and Linear Extendable Group Operated (MSP-LEGO) building blocks to achieve high efficiency and high power density in non-isolated high voltage conversion ratio dc-dc applications. Like other hybrid dc-dc solutions, the MSP-LEGO approach merges the strengths of switched-capacitor circuits and switched-inductor circuits, and facilitates series-input parallel-output configuration for balanced distribution of voltage stress and current sharing. The hybrid switched-capacitor-magnetics configuration enables zero-voltage-switching (ZVS) and near zero-current-switching (ZCS). The input voltage and output current of proposed architecture can be linearly extended through series-connected switched-capacitor circuits and parallel-connected switched-inductor circuits. A 100 W, 150 Vdc-to-5 Vdc non-isolated high conversion ratio hybrid dc-dc converter is built and tested. The prototype dc-dc converter achieved 110 W/in3 power density and 91.5% peak efficiency with automatic voltage balancing and current sharing.