An energy-conserving power-supply system utilizes a keep-alive DC power to consistently power a control circuit so as to render a main power supply readily actuatable for either distributing AC power or supplying regulated DC power. The energy-conserving power-supply system allows any one of modern information-processing or entertainment electronic products to be readily operable manually, remotely, or automatically from a standby state; while, it totally eliminates any unnecessary energy waste because AC power is neither transmitted nor wasted not only within but outside the power-supply system. The latter allows an external line-operated device to be concurrently operable from a no-power state, i.e., without consuming any standby energy at all. Not only can the energy-conserving power-supply system conserve energy usage to the greatest extent, it will also correspondingly extend the life spans of electronic circuitry and electromechanical components.