This question already has an answer here:
What I do have (default way of charging tablets: A) vs. what I want to have (B or C):
Can I have it?
It’s a simple thing, so why not?
How else can I use a tablet together with a portable hard disk (or with any USB device in fact) when I run out of battery power?
Marking my question as a duplicate of “Can I charge USB devices from a powered hub that isn't connected to a PC?” is wrong (as @AliChen explains on my behalf in a comment below).
In fact, I already use a USB hub connected to a universal USB charger to split electric power and charge multiple devices. And that hub is not even powered – it’s passive. So I know the answer to the other question very well – even without reading it.
This is different from using a single USB socket to charge a tablet and connect that tablet to a pendrive at the same time (presumably by the means of some kind of USB hub).