A power system (100D-B) comprising: a DC bus with a low side and a high side; a plurality of direct current, DC, to DC converters with outputs connected in series to form a series string between the low side and the high side of said DC bus, wherein each DC to DC converter comprises: a negative input terminal; a positive input terminal; a negative output terminal; and a positive output terminal, wherein each DC to DC converter is configurable to selectively operate in an upside-up buck mode of operation or in an upside-down buck mode of operation, wherein, in the upside-up buck mode of operation, the negative input terminal of the DC to DC converter is connected to the negative output terminal of the DC to DC converter, and the negative input terminal of the DC to DC converter has substantially the same voltage as the negative output terminal of the DC to DC converter, wherein, in the upside-down buck mode of operation, the positive input terminal of the DC to DC converter is connected to the positive output terminal of the DC to DC converter, and the positive input terminal of the DC to DC converter has substantially the same voltage as the positive output terminal of the DC to DC converter; wherein a first DC to DC converter which is configured in upside-down buck configuration is connected to the high side of the DC bus while any DC to DC converters between the first DC to DC converter and the high side of the DC bus are configured in a bypass state, and a second DC to DC converter which is configured in upside-up buck configuration is connected to the low side of the DC bus while any DC to DC converters between the second DC to DC converter and the low side of the DC bus are configured in a bypass state. a DC bus with a low side and a high side; a plurality of direct current, DC, to DC converters with outputs connected in series to form a series string between the low side and the high side of said DC bus, wherein each DC to DC converter comprises: a negative input terminal; a positive input terminal; a negative output terminal; and a positive output terminal, a negative input terminal; a positive input terminal; a negative output terminal; and a positive output terminal, wherein each DC to DC converter is configurable to selectively operate in an upside-up buck mode of operation or in an upside-down buck mode of operation, wherein, in the upside-up buck mode of operation, the negative input terminal of the DC to DC converter is connected to the negative output terminal of the DC to DC converter, and the negative input terminal of the DC to DC converter has substantially the same voltage as the negative output terminal of the DC to DC converter, wherein, in the upside-down buck mode of operation, the positive input terminal of the DC to DC converter is connected to the positive output terminal of the DC to DC converter, and the positive input terminal of the DC to DC converter has substantially the same voltage as the positive output terminal of the DC to DC converter; wherein a first DC to DC converter which is configured in upside-down buck configuration is connected to the high side of the DC bus while any DC to DC converters between the first DC to DC converter and the high side of the DC bus are configured in a bypass state, and a second DC to DC converter which is configured in upside-up buck configuration is connected to the low side of the DC bus while any DC to DC converters between the second DC to DC converter and the low side of the DC bus are configured in a bypass state.