This chapter examines modular systems for energy usage in computer and electrical/electronic applications. In recent years, the use of data centers and uninterrupted power supply for these centers are rapidly expanding. The chapter examines industrially available modular systems for these purposes. Modular high-performance computing systems are replacing large supercomputers, and these are described in detail in the chapter. The chapter also briefly examines Orion Energy Systems Compact Modular™ technology’s cooling properties for lighting system and Jenoptik modular energy systems for military platforms. In recent years, the use of micro- and miniscale electronic energy systems are rapidly increasing. The chapter examines power consumption and mode of operation of MNSs , micro- or nanotechnologies for energy harvesting such as solar energy, self-powered MNS and micropower management of solar energy harvesting using a modular platform. Finally, the chapter evaluates modular integrated power conversion and energy management system.