This research article discuss about the optimal fuzzy-PID controller tuned by hybrid differential evolution-particle swarm optimization (DEPSO) for automatic generation control of a two area multi-unit interconnected power system. Here the scaling parameters of the suggested controllers are tuned considering a step load perturbation (SLP) of 0.01p.u. in the area1.In each area of the scrutinized system three thermal units with reheat steam turbines and hydraulic amplifiers are considered where two distinct fuzzy-PID controllers are employed for automatic generation control. The dynamic behavior of the system is examined for various optimization methods and the supremacy of the suggested hybrid DEPSO method is established in terms of various time domain specifications like peak overshoots, undershoots and settling time. Later the robustness and sensitiveness of the proposed method is also established considering increased loading of the system.