A DSP-based active filter transient performance has been presented. Both the simulation results and the laboratory tests demonstrated the coherent performance of instantaneous reactive and oscillating active powers demanded by a three-phase AC/DC rectifier. Investigation where carried out to observe the active filter performance when its AC/DC inverter was fed either by a constant DC source, or by a previously charged DC capacitor. A superior performance was observed when the inverter was feed by a constant DC voltage source. However the DC capacitor fed inverter improves its performance considerably for a larger amount of instantaneous reactive power, as compared to the instantaneous oscillating active power demanded by non-linear load