Mains electricity in the context of AC adapter

Electric power is the rate of transfer of electrical energy within a circuit. Its SI unit is the watt, the general unit of power, defined as one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions of watts are called kilowatts, megawatts and gigawatts respectively.

In common parlance, electric power is the production and delivery of electrical energy, an essential public utility in much of the world. Electric power is usually produced by electric generators, but can also be supplied by sources such as electric batteries. It is usually supplied to businesses and homes (as domestic mains electricity) by the electric power industry through an electrical grid.

A microgrid is a local electrical grid with defined electrical boundaries, acting as a single and controllable entity. It is able to operate in grid-connected and off-grid modes. Microgrids may be linked as a cluster or operated as stand-alone or isolated microgrid which only operates off-the-grid not be connected to a wider electric power system. Very small microgrids are sometimes called nanogrids when they serve a single building or load.

A grid-connected microgrid normally operates connected to and synchronous with the traditional wide area synchronous grid (macrogrid), but is able to disconnect from the interconnected grid and to function autonomously in "island mode" as technical or economic conditions dictate. In this way, they improve the security of supply within the microgrid cell, and can supply emergency power, changing between island and connected modes. This kind of grid is called an islandable microgrid.

A drill is a tool used for making round holes or driving fasteners. It is fitted with a drill bit for making holes, or a screwdriver bit for securing fasteners. Historically, they were powered by hand, and later mains power, but cordless battery-powered drills are proliferating due to increased efficiency and ease of use.

Drills are commonly used in woodworking, metalworking, construction, machine tool fabrication, and utility projects. Specially designed versions are made for surgery, dentistry, miniatures, and other applications.

In electrical engineering, a light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresponding to the energy of the photons) is determined by the energy required for electrons to cross the band gap of the semiconductor. White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device.

Appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity infrared (IR) light. Infrared LEDs are used in remote-control circuits, such as those used with a wide variety of consumer electronics. The first visible-light LEDs were of low intensity and limited to red.

A lightbulb socket, lightbulb holder, light socket, lamp socket or lamp holder is a device which mechanically supports and provides electrical connections for a compatible electric lamp base. Sockets allow lamps to be safely and conveniently replaced (re-lamping). There are many different standards for lampholders, including early de facto standards and later standards created by various standards bodies. Many of the later standards conform to a general coding system in which a socket type is designated by a letter or abbreviation followed by a number.

The most common type of sockets for mains electricity are Edison screws, used in continental Europe and North America, while bayonet mounts dominate in the Commonwealth countries, except Canada, and in the automotive industry. Fluorescent lamps typically require a two-pin, unthreaded socket.

AC power plugs and sockets connect devices to mains electricity to supply them with electrical power. A plug is the connector attached to an electrically operated device, often via a cable. A socket (also known as a receptacle or outlet) is fixed in place, often on the internal walls of buildings, and is connected to an AC electrical circuit. Inserting ("plugging in") the plug into the socket allows the device to draw power from this circuit.

Plugs and wall-mounted sockets for portable appliances became available in the 1880s, to replace connections to light sockets. A proliferation of types were subsequently developed for both convenience and protection from electrical injury. Electrical plugs and sockets differ from one another in voltage and current rating, shape, size, and connector type. Different standard systems of plugs and sockets are used around the world, and many obsolete socket types are still found in older buildings.

An electrical cable is an assembly of one or more wires running side by side or bundled, which is used as an electrical conductor to carry electric current.

Electrical cables are used to connect two or more devices, enabling the transfer of electrical signals, power, or both from one device to the other. Physically, an electrical cable is an assembly consisting of one or more conductors with their own insulations and optional screens, individual coverings, assembly protection and protective covering.

An electric bus is a bus that is propelled using electric motors, as opposed to a conventional internal combustion engine. Electric buses can store the needed electrical energy on board, or be fed mains electricity continuously from an external source such as overhead lines. The majority of buses using on-board energy storage are battery electric buses (which is what this article mostly deals with), where the electric motor obtains energy from an onboard battery pack, although examples of other storage modes do exist, such as the gyrobus that uses flywheel energy storage. When electricity is not stored on board, it is supplied by contact with outside power supplies, for example, via a current collector (like the overhead conduction poles in trolleybuses), or with a ground-level power supply, or through inductive charging.

As of 2017, 99% of all battery electric buses in the world have been deployed in Mainland China, with more than 421,000 buses on the road, which is 17% of China's total bus fleet. For comparison, the United States had 300, and Europe had 2,250. By 2021, China's share of electric buses remained at 98% while Europe had reached 8,500 electric buses, with the largest fleet in Europe being Moscow.

A charging station, also known as a charge point, chargepoint, or electric vehicle supply equipment (EVSE), is a power supply device that supplies electrical power for recharging the on-board battery packs of plug-in electric vehicles (including battery electric vehicles, electric trucks, electric buses, neighborhood electric vehicles, and plug-in hybrid vehicles).

There are two main types of EV chargers: alternating current (AC) charging stations and direct current (DC) charging stations. Electric vehicle batteries can only be charged by direct current electricity, while most mains electricity is delivered from the power grid as alternating current. For this reason, most electric vehicles have a built-in AC-to-DC converter commonly known as the "on-board charger" (OBC). At an AC charging station, AC power from the grid is supplied to this onboard charger, which converts it into DC power to recharge the battery. DC chargers provide higher-power charging (which requires much larger AC-to-DC converters) by building the converter into the charging station to avoid size, weight and cost restrictions inside vehicles. The station then directly supplies DC power to the vehicle, bypassing the onboard converter. Most modern electric vehicles can accept both AC and DC power.

An electric shaver (also known as the dry razor, electric razor, or simply shaver) is a razor with an electrically powered rotating or oscillating blade. The electric shaver usually does not require the use of shaving cream, soap, or water, known as dry shaving, although many users still prefer a skin lubricant for comfort.

The razor may be powered by a small DC motor, which is either powered by batteries or mains electricity. Many modern ones are powered using rechargeable batteries. Alternatively, an electro-mechanical oscillator driven by an AC-energized solenoid may be used. Some very early mechanical shavers had no electric motor and had to be powered by hand, for example by pulling a cord to drive a flywheel.

In electrical engineering, a light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, thereby releasing energy in the form of photons. The color of the light (corresponding to the energy of the photons) is determined by the energy required for electrons to cross the band gap of the semiconductor. White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device.

Appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity infrared (IR) light. Infrared LEDs are used in remote-control circuits, such as those used with a wide variety of consumer electronics. The first visible-light LEDs were of low intensity and limited to red.

A power supply unit (PSU) converts mains AC to low-voltage regulated DC power for the internal components of a desktop computer. Modern personal computers universally use switched-mode power supplies. Some power supplies have a manual switch for selecting input voltage, while others automatically adapt to the main voltage.

Most modern desktop personal computer power supplies conform to the ATX specification, which includes form factor and voltage tolerances. While an ATX power supply is connected to the mains supply, it always provides a 5-volt standby (5VSB) power so that the standby functions on the computer and certain peripherals are powered. ATX power supplies are turned on and off by a signal from the motherboard. They also provide a signal to the motherboard to indicate when the DC voltages are in spec, so that the computer is able to safely power up and boot. The most recent ATX PSU standard is version 3.1 as of mid 2025.

An uninterruptible power supply (UPS) or uninterruptible power source is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions, by supplying energy stored in batteries, supercapacitors, or flywheels.

The on-battery run-time of most uninterruptible power sources is relatively short (typically ranging from 5 to 15 minutes) but sufficient to start a standby power source or properly shut down the protected equipment. It is a type of continual power system. A UPS is typically used to protect hardware such as computers, data centers, telecommunication equipment or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption or data loss. UPS units range in size from units designed to protect a single computer without a video monitor (around 200 volt-ampere rating) to large units powering entire data centers or buildings.