Thanks for the question about the Plugable 7-Port USB Hub with 3A AC Adapter.
I’m using this hub on a Mac right now as I type. Compatibility with Mac is no problem.
It doesn’t, however, support any extensions beyond the USB 2.0 specification. What that means in the case of the iPad is the hub is able to supply the max USB 2.0 bus power (500mA) easily to the iPad - including in combination with other higher-power devices you might attach to the hub.
But Apple also has a USB 2.0 behavioral extension which they’ve implemented on recent Macs that allows them to detect a device which wants to get more than 500mA, and supply it.
Apple has a description here: http://support.apple.com/kb/HT4049
The Plugable hub doesn’t support those special extensions. So, when you plug in an iPad, it will get the full 500mA, but no more. The iPad will charge at 500mA rate when turned off, and will report “Not Charging” when its screen is turned on, because the iPad needs more than USB 2.0 spec power, to both charge and be on at the same time.
I hope that answers the question fully. Thank you!