This invention concerns power supplies suitable for electric arc gas heaters such a plasma torches. It more particularly relates to the dimensioning of the inductor in the switched-mode DC to DC converter used for feeding the torch. The invention concerns in particular a DC power supply for driving a non-transferred electric arc gas heater, comprising: an AC to DC rectifier providing a potential U0; a DC to DC switching converter having a switching frequency fS; a current control loop having a latency Formula (I); and, a ballast inductor having an inductance L; characterized in that inductance L is such that Formula (II) and Formula (III). Such a design ensures the stability of the current control loop, while also ensuring a sufficient amount of current ripple to spread out the erosion zone on the electrodes of the torch. τ ; ( I ) L > ( U 0 1500 ) ⁢ τ , ( II ) L