A controller for determining a distribution of switching phases among switching elements of a power supply system, the power supply system comprising a plurality, N, of voltage converters (200-1 to 200-N), wherein each voltage converter comprises a respective one of the switching elements and is arranged to convert an input voltage (Vin) supplied to the voltage converters to a respective output voltage (Vout 1 to Vout N) by applying a control pulse to the respective switching element at a predetermined switching frequency, f, so as to switch the switching element ON for the duration of the control pulse during a switching period 1/f, wherein the sum of the pulse durations of the control pulses used by the plurality of voltage converters in the switching period is smaller than the switching period, the controller comprising: a receiver for receiving one or more signals indicative of a respective contribution from each of the voltage converters (200-1 to 200-N) to a ripple current component of an input current of the voltage converters; a switching phase offset calculator configured to calculate, based on the received one or more signals, a respective switching phase offset that is to be applied for the switching element in each of the voltage converters (200-1 to 200-N) by: determining a switching order in which the switching elements of the respective voltage converters are to be switched ON during a switching period, by assigning to each j th position in the switching order, where j = 1, 2,... N, a respective one of the voltage converters using the expression f j = j + 1 2 1 + − 1 j + 1 2 + N − j − 2 2 1 + − 1 j 2, where f ( j) represents the position, in a ranking of the voltage converters in order of decreasing contribution to the ripple current component, of the voltage converter for position j in the switching order; and arranging the control pulses of the voltage converters within the switching period in accordance with the determined switching order such that the period of time between each adjacent pair of control pulses in the switching period is the same; and an output signal generator configured to generate one or more output signals defining the calculated switching phase offsets to be applied to the switching of the respective switching elements. a receiver for receiving one or more signals indicative of a respective contribution from each of the voltage converters (200-1 to 200-N) to a ripple current component of an input current of the voltage converters; a switching phase offset calculator configured to calculate, based on the received one or more signals, a respective switching phase offset that is to be applied for the switching element in each of the voltage converters (200-1 to 200-N) by: determining a switching order in which the switching elements of the respective voltage converters are to be switched ON during a switching period, by assigning to each j th position in the switching order, where j = 1, 2,... N, a respective one of the voltage converters using the expression f j = j + 1 2 1 + − 1 j + 1 2 + N − j − 2 2 1 + − 1 j 2, where f ( j) represents the position, in a ranking of the voltage converters in order of decreasing contribution to the ripple current component, of the voltage converter for position j in the switching order; and arranging the control pulses of the voltage converters within the switching period in accordance with the determined switching order such that the period of time between each adjacent pair of control pulses in the switching period is the same; and determining a switching order in which the switching elements of the respective voltage converters are to be switched ON during a switching period, by assigning to each j th position in the switching order, where j = 1, 2,... N, a respective one of the voltage converters using the expression f j = j + 1 2 1 + − 1 j + 1 2 + N − j − 2 2 1 + − 1 j 2, where f ( j) represents the position, in a ranking of the voltage converters in order of decreasing contribution to the ripple current component, of the voltage converter for position j in the switching order; and arranging the control pulses of the voltage converters within the switching period in accordance with the determined switching order such that the period of time between each adjacent pair of control pulses in the switching period is the same; and an output signal generator configured to generate one or more output signals defining the calculated switching phase offsets to be applied to the switching of the respective switching elements.