An universal active power filter controller system is proposed that adapts itself to both harmonic current source type loads as well as harmonic voltage source type loads is presented in this paper. The system level harmonic filtering application issues of a multiple and clustered harmonic producing load site, such as at an industrial load site or at a distribution substation, are addressed. Harmonic filtering solution for such sites is especially complicated because the overall site load characteristics can change from a harmonic current source type to a harmonic voltage source type load, depending on the operating point of the various individual loads. The proposed hybrid series active filter (HSAF) solution provides harmonic filtering for harmonic current source type load characteristics, and degrades controllably to a 'pure' series active filter (SAF) to provide harmonic filtering for harmonic voltage source type load characteristics. Both the HSAF and SAF are controlled by synchronous reference frame (SRF) controller. Field test results validate the adaptability and effectiveness of the proposed HSAF/SAF system for a 480 V, 750 kVA multiple and clustered load site.