USB charger FAQs

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What is a USB charging port?

USB stands for Universal Serial Bus (USB), with the computing term ‘bus’ referring to a system that transfers data either between computers or between components within a computer.

Ports are used to connect one device to another. Such devices include: computer mice, smart phones, printers and keyboards.

In order to allow these devices to function, the USB port also transfers an amount of electrical current from the main (powered) device (the host) to its peripheral devices.

How does a USB charger work?

A USB network has a host and a device. The host is usually either a PC or a power module that allows charging directly from the power supply.

USBs transfer both data and power. Traditionally, power only flowed in one direction — from the host to the device. However, advances in power delivery technology means that can be transferred in both directions.

The most common type of USB port features 4 pins, matching the 4 wires found in the USB charging cable. The pins on the inside allow data to transfer, while the out pins carry the electrical current. A later version of USB includes another 5 pins, with compatible charging cables that feature an extra 5 wires.

There are 3 main types of charging port. They are as follows:

USB port type Power output Devices that feature port

Standard Downstream Port (SDP)

0.1A when connected

0.5A when configured for high power

PC, laptop

Downstream Port (CDP)

Up to 1.5A

PC, laptop

Dedicated Charging Port (DCP)

More than 1.5A, according to charging device

USB power module, wall charger

Can a USB power module charge multiple devices?

Yes. USB power modules are designed to be able to charge multiple devices at the same time.

While voltage will be standard across the different USB ports, some modules ‘share’ their current across ports. This may result in slower charging times when more devices are connected.

Also keep in mind that different devices have different optimum currents from which to charge. Charging with a lower-than-optimum current can reduce charging time.

Why are some USB chargers faster than others?

This relates to the current that a charging point supplies, measured in amps.

Both voltage and current affect how quickly a device will charge. In order to protect electronic equipment from overloading, chargers take the UK’s 240V electricity supply and convert it to a standard 5V.

However, the current (in amps) can vary from charging source to charging source. Computers typically only allow 0.5A of current, making charging quite slow and laborious. Plugs into which you insert a USB charging cord usually offer 1A. Specialised USB charging modules can offer anything from 1–5A.

The cable that you use to charge a device can also affect speed. Thinner cables reduce amperage, leading to longer charging times.

What is the power output from a computer USB port?

Most computer USB ports supply 5V of electricity with a maximum current of 0.5A. This amount of current is standard across the majority of computers and means the overall power output will be 2.5 Watts at best. Later USB designs bring that current up to 0.9A. However, most devices attached to a computer’s USB port will only draw out 0.1A of power unless more is required.

USB ports and cables — an overview

USB has seen a number of versions over the years, both in terms physical port shape and charging/data transfer speeds. Depending on the age of your device, you may have one or several versions of USB ports on your devices.

The following tables look at the major versions and their specifications:

USB versions

Version Name Release date Transmission rate

USB 1.1

Full Speed USB


12 Mbps

USB 2.0

High Speed USB


480 Mbps

USB 3.0

SuperSpeed USB


5 Gbps

USB 3.1



10 Gbps

Most people will be more familiar with the physical shape of USB connectors. These typically feature a flat rectangular plug (the male connector) at one end that fits into the port on your computer or power module (the receptacle). The other end of a charging wire will either feature the same type of plug, or one of several shapes that have developed over the years for connecting to different devices.

The table below looks at some of these plugs:

USB cable type Image Official name Description Compatibility


USB Standard-A

By far the most common type. This will feature on one end of nearly all USB cables.

USB 1/2/3 type as all compatible with each other


USB Standard-B

This square-shaped plug is often used to connect computers with printers, scanners or similar devices.

USB 1/2 type B plugs compatible with USB 1/2/3 receptacle. USB 3.0 plug only compatible with USB 3 receptacle


USB Type C

The latest addition to the USB family, this plug works like a standard smartphone charger but is horizontally symmetrical, meaning it can be put in ‘upside down’.

As it is the latest type, the USB-C shape is only produced in USB 3.1

USB-Mini B

USB-Mini B

These plugs were used for charging older mobile phones, cameras and MP3s but are largely redundant now.

USB Mini-B plugs work with USB 2.0 Mini-B and Mini-AB receptacles

USB-micro B


The USB 2 micro B is the standard plug shape found on all modern Android smartphones.

USB 2.0 micro B plugs can fit into USB 3 micro B receptacles but USB 3.0 micro B plugs cannot fit into USB 2 micro B receptacles

USB 3.0 micro B

Micro-B SuperSpeed

The new USB 3 micro B is capable of transferring extra data.

USB 3.0 micro-B plugs will only fit with either USB 3.0 micro-B receptacles or USB 3.0 micro-AB receptacles