The benefit of USB charging is that it allows the charging of all portable devices. The devices charged may even be extended to cameras, handy cams, iPhones, iPads, iPods, music players, etc. USB charger refers to those chargers that are used to charge mobiles or batteries in general via USB cables. USB charger is different from the regular wall charger that comes with the mobile phones. These two terms are often confused as one and the same.
The USB power supply through the USB cable aims at an output of 5V direct current, irrespective of the device it is plugged into. Most USB power supplies deliver an output of 0.5 A, the common USB 2.0., that is. USB 3.0 can deliver an output close to 1.0 A while some can even go up to 2.0 A.
Unlike the USB power supplier or wall charger, a well designed and optimum USB charger is built to specifically charge batteries of portable devices with utmost safety and care.
USB chargers are basically of two types; Ego/cigar like chargers or integrated chargers. Ego or cigar like chargers usually comes with smaller, non-replaceable batteries. Integrated chargers usually are inbuilt. See here to learn more about USB chargers.
Here we discuss the two main types of USB chargers:
Ego or cigar-like style chargers: These chargers are designed to specifically match certain batteries. They cannot be randomly paired with any battery, meaning they cannot be used to charge just about any battery. Misuse poses a threat to the device and the user. They are even capable of causing fires. It would be best to get these chargers from reliable and known companies to avoid risk.
Integrated chargers: these are the chargers that can neither be fooled nor misplaced as they are inbuilt in the specific device. Being inbuilt in the device implies that they are small in size and weigh only around a gram or so.
Ideal USB chargers know how much current it can draw from a system and can cut out power supply once the device is fully charged. If a device attempts to draw current higher than the capability of the supply, it risks overloading the USB port which will most probably shut down, blow a fuse or harm the device and system too. An ideal charger connects to the system through software that enables port detection and can handle the hardware and safety issues of charging the device and is equipped to keep the device safe.
USB chargers may be built such that the battery may be charged when in use by the device or by disconnecting the battery from the device. When the battery is charged by disconnecting from the device, it can be charged faster. USB chargers can also determine if the right kind of batteries are inserted, else cuts off connection and keeps the device safe.
It is always best to follow the OEM specifications and stick by them so as to not risk damaging your device. Proper caution and knowledge of the charger and equipment will increase the life of the device.