Add a large resistance to achieve a significant voltage drop. Use the damping resistor, it can be purchased in specialized departments or to collect yourself. However, the use of so-called damping resistor, as resistance leads to a nonsensical allocation of it capacity.
For AC systems use reactive damping impedances, usually capacitors, so the capacitor power supply.
In addition to lower voltage circuit without transformer, you can use thyristor regulators. Typically, use ready-made controllers to collect yourself is almost pointless), an electronic circuit which allows you to change the input to the load output with controlled turn-on delay of the thyristor half cycle of the alternating current.