A power supply cell of a power supply system including a first power conversion circuit to output a first DC voltage, a second power conversion circuit to output a second DC voltage, a first controllable unidirectional semiconductor switch to generate a first conduction path from the first power conversion circuit to the second power conversion circuit, a first unidirectional semiconductor switch to generate a second conduction path from the first power conversion circuit to the second power conversion circuit, a second unidirectional semiconductor switch to generate a third conduction path from the first power conversion circuit to the second power conversion circuit, a first low-pass filter, and a controlling unit operative to issue turn-on signal or turn-off signal to the first controllable unidirectional semiconductor switch to supply current to the low-pass filter via the first conduction path or both of the second conduction path and the third conduction path.