A power supply system (1, 1#) having a plurality of rechargeable power storage units (BAT1, BAT2 to BATN), comprising: a power line (MPL, MNL) configured to allow supply and reception of electric power between a load device and said power supply system (1, 1'#); a plurality of voltage conversion units (CONV1, CONV2 to CONVN) provided between said plurality of power storage units (BAT1, BAT2 to BATN) and said power line (MPL, MNL), respectively, and each adapted to perform voltage conversion operation between corresponding said power storage unit (BAT1, BAT2 to BATN) and said power line (MPL, MNL); and voltage reference value determination means (50, 52, 54) configured to determine a voltage reference value (Vh*) as a voltage required to be supplied by said power line (MPL, MNL) to said load device in accordance with an operation status of said load device, wherein each of said plurality of voltage conversion units (CONV1, CONV2 to CONVN) is configured to perform said voltage conversion operation so as to match its supply voltage value with said voltage reference value (Vh*) determined by said voltage reference value determination means (50, 52, 54), characterized in that the power supply system (1, 1#) comprises power storage voltage value obtaining means (12-1, 12-2 to 12-N) adapted to obtain a power storage voltage value (Vb1, Vb2) for each of said plurality of power storage units (BAT1, BAT2 to BATN), wherein said voltage reference value determination means (50, 52, 54) is configured to limit said voltage reference value (Vh*) not to fall below the maximum power storage voltage value of said power storage voltage values (Vb1, Vb2) obtained by said power storage voltage value obtaining means (12-1, 12-2 to 12-N). a power line (MPL, MNL) configured to allow supply and reception of electric power between a load device and said power supply system (1, 1'#); a plurality of voltage conversion units (CONV1, CONV2 to CONVN) provided between said plurality of power storage units (BAT1, BAT2 to BATN) and said power line (MPL, MNL), respectively, and each adapted to perform voltage conversion operation between corresponding said power storage unit (BAT1, BAT2 to BATN) and said power line (MPL, MNL); and voltage reference value determination means (50, 52, 54) configured to determine a voltage reference value (Vh*) as a voltage required to be supplied by said power line (MPL, MNL) to said load device in accordance with an operation status of said load device, wherein each of said plurality of voltage conversion units (CONV1, CONV2 to CONVN) is configured to perform said voltage conversion operation so as to match its supply voltage value with said voltage reference value (Vh*) determined by said voltage reference value determination means (50, 52, 54), characterized in that the power supply system (1, 1#) comprises power storage voltage value obtaining means (12-1, 12-2 to 12-N) adapted to obtain a power storage voltage value (Vb1, Vb2) for each of said plurality of power storage units (BAT1, BAT2 to BATN), wherein said voltage reference value determination means (50, 52, 54) is configured to limit said voltage reference value (Vh*) not to fall below the maximum power storage voltage value of said power storage voltage values (Vb1, Vb2) obtained by said power storage voltage value obtaining means (12-1, 12-2 to 12-N).