Chapter 1 motivated the suitability of switched-capacitor converters (SCCs) for achieving a high input voltage ( \({\sim }400\,\mathrm {V}\) ) and complete integration within the milliwatt power range. Therefore, in Chap. 2 , the fundamentals of SCCs were elucidated. However, state-of-the-art fully integrated SCCs are confined to a maximum input voltage of 42 V. This chapter targets to push this maximum input voltage to 400 V DC. The proposed topology overcomes the key challenges associated with the increasing input voltage, which include diminished component quality and heightened parasitic losses. This chapter starts by elaborating on the specifications and discussing the shortcomings of state-of-the-art approaches. The following part examines the key challenges at high input voltages and proposes a topology to tackle these challenges. Subsequently, the implementation details are covered, including the customization of high-voltage capacitors and drivers, as well as an improved control circuit. Finally, Sect. 3.6 presents the measurement results and compares them with the state of the art.