This article presents the results of experiments aimed at studying the conditions for the excitation of current and voltage oscillations in plasma in a three-electrode voltage stabilizer. It was found that in the modes under consideration, the plasma had negative conductivity, which caused oscillations. We propose a highly efficient method for suppressing instabilities that is based on controlling the sign of the plasma’s differential conductivity via adjusting the concentration of the plasma’s thermal electrons with an external control electrode. The proposed method makes it possible to achieve a high level of stability of the energy parameters of voltage stabilizers and those of other plasma-based devices.