The theoretical analysis of quadratic correlations of equilibrium electrical fluctuations in the Markovian electrochemical ac circuit is accomplished. The modified Fokker-Plank equation which allows one to follow the time evolution of 2nd-order correlators of electrochemical stochastic diffusion associated with the Markovian electrochemical ac circuit (Eq. (7)) is obtained. Due to interdisciplinary significance of the random process theory, the resulting Fokker-Planck equation is also of certain interest for the general theory of stochastic phenomena occurring near the equilibrium state. The derived modified Fokker-Planck equation can be used in the electrochemical noise diagnosis as the Markovian standard of electrochemical stochastic diffusion.