The 61600 and 61500 function the same, however, the 61500 AC power source is equipped with more features. It allows you to compose different harmonic components to synthesize your own harmonic distorted wave-shapes. Features included are power line disturbance simulation, programmable output impedance, comprehensive measurement functions, harmonics & inter-harmonics wave-shape synthesis, voltage dips and variation simulation, and high output current crest factor.