A power source system comprising; a first direct current power source, a second direct current power source, a power converter including a plurality of switching elements (S1-S4) for performing direct current power conversion between a power source line electrically connected to a load, the first and the second direct current power sources (10, 20), and a control device configured to control on-off of the plurality of switching elements in accordance with a pulse width modulation control for controlling an output voltage (Vo) on the power source line, wherein the plurality of switching elements are disposed to be included in both a first power conversion path formed between the first direct current power source and the power source line, and a second power conversion path formed between the second direct current power source and the power source line, wherein the power converter has a first operation mode for performing the direct current power conversion between the first and second direct current power sources and the power source line in parallel, wherein the control device is configured to vary a phase difference (ø) between a first carrier signal used for a first pulse width modulation control to control a first power conversion via the first power conversion path, and a second carrier signal used for a second pulse width modulation control to control a second power conversion via the second power conversion path in the first operation mode, according to an operation condition of the power converter, and wherein the control device is configured to generate control signals (SG1-SG4) of on-off of the plurality of switching elements on the basis of a first control pulse signal (SDa) obtained by the first pulse width modulation control and a second control pulse signal (SDb) obtained by the second pulse width modulation control, and wherein the plurality of switching elements (S1-S4) includes a first switching element electrically connected between the power source line and a first node, a second switching element electrically connected between a second node and the first node, a third switching element electrically connected between the second node and a third node electrically connected to a negative electrode terminal of the second direct current power source, and a fourth switching element electrically connected between a negative electrode terminal of the first direct current power source and the third node, and wherein the power converter further includes a second reactor electrically connected between a positive electrode terminal of the second direct current power source and the first node, characterised by further including a first reactor electrically connected between a positive electrode terminal of the first direct current power source and the second node, and wherein the control device is configured to generate control signals (SG1-SG4) such that: - the first power conversion path is switched between a path that passes through the third switching element and the fourth switching element, and a path that passes through the first switching element and the second switching element; and - the second power conversion path is switched between a path that passes through the first switching element and the fourth switching element and a path that passes through the second switching element and the third switching element. - the first power conversion path is switched between a path that passes through the third switching element and the fourth switching element, and a path that passes through the first switching element and the second switching element; and - the second power conversion path is switched between a path that passes through the first switching element and the fourth switching element and a path that passes through the second switching element and the third switching element.