The invention relates to a power adjustment system adapted for powering an electric line for supplying power to vehicles moving in a traffic lane combined with said electric line that comprises an electric supply feeder (AD) delivering an average electric power directly or via at least one converter to the electric line, and an adjustable power based on power fluctuation and required for an instantaneous traffic intensity to an energy storage means (MS) capable of powering the electric line at a peak power via at least one other converter, characterised in that a dimensioning unit (PCC) receives information on the power needs based on the traffic intensity evaluated over at least one duration of said traffic, and in that the dimensioning unit uses information for controlling an adjustment of the useful predictable storage of the storage means so that the electric power (P_IN0, P_IN1) delivered to the storage means is adjusted and minimal while exactly maintaining a sufficient energy backup in the storage means for compensating for any peak power (P_INST) instantaneously required by the traffic in the given duration.