In this paper, we present an extension of the ANC (“Analogue Network of Converters”)-based method to characterize the harmonic components of a set of converters with random-phase harmonics using only digital test resources. The ANC-based method was primarily developed under the assumption that the harmonics' phase is proportional to the input phase. This assumption is not valid for all converter architectures, where filtering effects may affect the harmonics'phase. The improved ANC-based method is able to calculate the magnitude of the harmonic components regardless of their phase. The simulation results and the experiments show an excellent agreement between the values measured using the method and the values measured with a usual test setup, for the THD and SFDR parameters.