USB Power Supplies
USB power supplies are designed to provide a DC output of 5 volts. These power supplies are sold without a USB lead and are suitable for charging all USB devices. It is essential, though, that the output power or output current is at least as high as that required by the device or it will not be possible to fully or quickly charge a device. Many newer USB powered devices need an output current of 1 amp and some high-powered phones and tablets need a USB power supply capable of supplying more than 2 amps (12 watts). If you have lots of devices that need to be charged, consider buying a dual USB charger with two or even four USB outputs. Just bear in mind that the output power specified for dual or quad USB chargers will limit how much power can be drawn, and some multiple USB chargers have only one high-power USB socket. USB power supplies are not suitable for powering other DC powered equipment, and a universal AC/DC Plug-in Power supply is needed. Most USB power supplies are mains operated, although DC powered USB power supplies are also available. Manufacturers of USB power supplies include Ansmann, Friwo and Nordic Power.