"Energy Regulator"?...

...!
In some countries with an unstable/unpredictable Mains Power Supply, you may require the use of an external "Voltage Regulator" to ensure a stable Voltage to your equipment.
The other device which is sometimes used, is a "Surge Protector", mainly to prevent damage from Lightning Strikes to the Power Lines, creating high Voltages in the Power Supply, and damaging your equipment.
In Great Britain, our Mains Supply Voltages and Frequencies are maintained within very strict, closely controlled