An electric power source arrangement is described, comprising a fuel cell means (2) having a nominal voltage and a specified voltage-current characteristic, to be connected to a load (1), and comprising a variable DC-DC voltage converter (3), a by-pass branch (11) by-passing the DC-DC voltage converter, a switch (13) alternatively connecting the fuel cell to the DC-DC voltage converter or to the by-pass branch, and a control unit (12) controlling the switch, which control unit (12) comprises a measuring device coupled to the fuel cell means (2) for detecting the operating point thereof and is configured to connect the by-pass branch (11) if the fuel cell means voltage is within a selected range of section (5) of the voltage-current characteristic of the fuel cell means and to disconnect the by-pass branch in the remaining range of sections (4, 6, 7) of said characteristic.