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Connecting converters in cascade is a basic configuration of dc distributed power systems (DPS). The impedance interaction between individually designed converters may make the cascaded system unstable. The previous presented approaches of stabilizing the cascaded systems need to modify the source and/or load converter's internal structure such as the topology and control circuit that are contradictory to the modularization characteristic of dc DPS. In this paper, an adaptive active capacitor converter (AACC) is introduced to stabilize the cascaded system. The AACC is connected in parallel with the cascaded system's intermediate bus and only needs to detect the bus voltage without any change of the existing subsystems. Hence, it can be designed as a standard module for dc DPS. The AACC serves as an equivalent bus capacitor to reduce the output impedance of the source converter, thus avoiding the intersection with the load converter's input impedance, and as a result, the cascaded system becomes stable. The equivalent bus capacitor emulated by the AACC is adaptive according to the output power of the cascaded system, and thus, the power loss of AACC is minimized and the dynamic response of the system is better than that of the system using a passive capacitor. Furthermore, since no electrolytic capacitor is needed in the AACC, the cascaded system's lifetime is prolonged. The operation principle, control, and design consideration of the AACC are discussed in this paper, and a 480 W cascaded system comprising two phase-shifted full-bridge converters has been built and evaluated. The experimental results verify the validity of the proposed AACC.