It is very common for some people to charge their iPhone or ipod from mac or a PC but when you connect an ipad with your computer it won't charge and display "Not Charging" in the charging section.
Charging the iPad through USB hub of your computer might cause this problem. It is a more common problem with the older Macs but there are a few cases on newer Macs.
- If the problem is with the adapter try removing all the dust from USB or change to a newer USB cable.
- While charging with Mac put the iPad in sleep mode and make sure the Mac is awake.
- If the iPad is not charging at all with any charger than it is due to the battery problem you should try to change the battery.
- Try to restart your device using the on/off button.