In this paper we discuss the Hawking's evaporation of the masses of variable-charged Reissner–Nordstrom and Kerr–Newman black holes embedded into the de Sitter cosmological universe by considering the charge to be function of radial coordinate. It has been shown that every electrical radiation of variable-charged rotating or non-rotating cosmological black holes will produce a change in the mass of the body without effecting the Maxwell scalar and the cosmological constant. It is also shown that during the Hawking's radiation process, after the complete evaporation of masses of both variable-charged Reissner–Nordstrom–de Sitter and Kerr–Newman–de Sitter black holes, the electrical radiation will continue creating negative mass naked singularities embedded into de Sitter cosmological spaces.