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Very very few tablets or phones can charge from the USB socket when it's in USB2Go host mode connecting to a hub, keyboard or anything. Most only charge (take external power AT ALL) when in slave mode, to a charger or a USB host port.
It's not an Android issue. It's a non-standard hardware design on some phones and tablets. Some are Windows and some are Android.
I have two special power splitter cables. One only works with the special hardware of phone or tablet. The other is simply powering a slave device from your charger to save the tablet battery, which a powered hub can also do. Neither the in port of a hub, nor the splitter cable will power the phone or tablet.
You can simply uses a BT keyboard and have the ink tablet on the charger. If it's properly designed it won't do it any harm. Similarly you can charge the BT Keyboard from a separate charger or a dual outlet charger. There is no point to a hub.
Any OUT port on a hub can charge the tablet, but it is then in slave mode and can't connect to the OUT port with a USB keyboard.
A few current tablets (not eink) do have a separate coax socket for power. Mostly those are the only ones that can use USB slave devices and charge.
Few BT keyboards are as good as a USB slave.
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