Autotransformers for voltage boost, voltage reduction and output voltage balancing of separate phases ("step-up", "step-down" and divided phase), transformers of toroidal insulators essential in professional marine power supplies to prevent electrolytic corrosion and guarantee a safe electrical system and low-cost galvanic insulators to prevent corrosion that occurs in ships with electrical power, blocking low voltage DC currents entering the boat through the ground wire of the shore power.