A transformer is any device used to change the voltage level of electric current. Transformers can either increase or decrease voltage. Step-up transformers are used in commercial energy provision to boost voltage levels prior to transmission of electricity through high tension lines or underground cables, and they are also found in consumer electronics products such as televisions where they convert standard household current to the high voltages needed by cathode ray picture tubes. Transformers can range in size from a tiny fraction of a cubic inch to the size of a small office building. Large transformers used by energy providers are usually divided into two classes: vault and padmount. Vault transformers are usually constructed in underground chambers (vaults) and covered by metal grilles which allow heat generated by the transformer to escape. Padmount transformers are mounted on concrete pads, and are typically fenced off to protect the transformer, passing wildlife and the general public.

Converters are devices that convert power between alternating current (AC) and direct current (DC). AC/DC converters convert power from AC to DC, and these are most commonly used by consumer devices that require direct current for their operation. The process of conversion is usually preceded by a change in the voltage to a required level for the device. Most of the plug-in adapter devices used by household and commercial appliances and referred to as wall warts are combination transformer/converter devices.

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