Adapters: DC Barrel, USB to DC etc.
Types of DC barrel connectors
DC barrel connectors are also known as coaxial, tip or concentric connectors. They are used to connect extremely low voltage appliances
or devices to an external source of electricity. Some of them come with a switch that is used to cut the circuit completed by internal battery sources whenever an external source of power comes into play.
These connectors come in a range of sizes and their ratings are anywhere between 1 and 5 amperes. Specially powered versions can handle as many as 11 amperes. The two most common plugs have an inside diameter of 5.5mm. Another common barrel connector is the 3.5mm type, which is mostly used in extremely low voltage situations.
Standards: The most common standards are EIAJ, DIN and IEC.
DC Power over USB cables
Direct Current power, also known as DC power, is popular for mobile device charging because it is easily stored in batteries.
All USB cables push DC power at up to 5 volts, but the amperage can vary. A standard USB-3 cable is rated to carry 900mA at 5 volts. Older USB-1 and -2 cables were rated for 500mA at 5 volts. Power Delivery (PD) cables, including Apple iPad chargers, push 2,100mA at 5 volts, while Kindle Fire chargers output 1,800mA at 5 volts. Many car chargers output 1,000-1,200mA at 5 volts.
USB charging ports, whether plugged into AC or DC power sources, can be rated up to 3,000mA. Don't be alarmed, though. There is no danger of damaging your USB cables or devices by plugging cables into more powerful ports. Any USB cable can safely be connected to any USB port. A higher-amp port may even charge your device faster, depending on its age.
USB technology limits cable length to 5 meters, but much shorter cables like the one included with your device are optimal for charging. Resistance increases over longer cable lengths, so extra-long USB cables will diminish voltage. Two amps run through a 2-meter USB cable diminishes the voltage by .77v if the cable uses a standard 28 gauge wire. Hardier cables with 24-gauge wire will lose only .3v over the same distance and amperage. Plug adaptors and connectors do not significantly impact the voltage.