The old USB standards
USB standard 1.0 and 2.0 must deliver 5 volts (V) and at least 500 milliamps (mA) per USB port.
Older USB phone chargers deliver between 700mA and 1000mA so they can power one or maybe two 500mA devices. How do you know what mA they deliver? Get a magnifying glass and look at the fine print – it should have an output of 5V and XXXX mA (1000 mA = 1 AMP) printed on the charger.
Note that there is no issue with using a higher mA rated charger on any USB device – as long as there is enough mA to drive your devices i.e. a keyboard and mouse takes far less mA than an external hard disk.
Now to the new standards
The new USB 3.0 standard requires 900 mA (.9A) per port.
There is a newish battery charger USB standard that allows the device to fast charge if there is sufficient mA or it goes into trickle or no charge mode.
A lot of new smartphones, tablets, eReaders and cameras now require at least 1.5A and many the entire 2.1A in order to fast charge.
Result - these devices may not charge or take too long to charge when plugged into older chargers, computer or monitor outputs.
What can you do?
The average home or office is littered with old chargers so get the magnifying glass out and check. Then check the requirements of your devices and match these to them. Best thing to do is to dispose of the older chargers and buy new 2.1A or greater ones.
But what if you need to use an older 500mA port on a charger, PC, USB hub or monitor. iStyle has a PowerPill that will take that and ramp it up to 2.1A.
The model I tested has different modes for each device: Blue for iPad/iPad mini; Red for Galaxy Tab, Notes; and LED off for data sync. It simply plugs inline using your standard USB to micro cable. According to the specifications it will charge a Samsung S3 in three hours as compared to six hours on trickle. And it will charge an iPad and Galaxy Tab 10.1 from a standard port where without it the device will not charge at all. RRP $29.95 on-line and from major retailers.