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So, I have been tethering my tablet with my PC for a long time and I noticed that It charges pretty fast when connected through USB hub compared to normal tethering on USB 3.0 port. I installed Ampere app on tab and found out that it was charging at about 1300mA! Whereas the maximum power output of USB 3.0 should be no more than 900mA! What is happening?? Sometimes when I replug it, It starts charging at only 400-500mA sometimes even lower but mostly over 1000! However, what boggles my mind the most is that this number is after deducting the load (power usage of device itself) which is usually around 250-300mA (I know this because whenever I adjust the brightness from 20-100%, the current drops drastically to only 200-300mAh because of this huge very bright display and when its not charging at that time load also jumps about 800mA higher when I suddenly put it at max brightness peaking at 1240~1400mA ), which means total power input is even higher than what Ampere APP is showing! USB 2.0 ports seem to be working fine at around 500mA which is what I expected but USB 3.0 to hub seems to be acting weird..

The final bit that makes it even more confusing is that on the BOX of USB HUB that I am using, It is especially mentioned "Maximum Current 500mA Per Port" !! This doesn't make sense at all because when connected to the original charger of the tab (18W which is about 2800~3000mA in Ampere app) via USB hub, it again puts out 1600mA + Load (150-200mA under idle) consistently which is way more than 500mA limit.. Its a NON POWERED HUB at that!!

Why is this happening? and Although I don't want to fix it because rather than a bug, feels more like a feature, However I still want to know if it poses any risk to either my PC or the Tablet??

At all times, tablet is the only thing connected to the HUB with just 1 port used out of total 4

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    More likely than not, this is unanswerable unless someone reviews the PCB schematics of the hub, which aren't publicly accessible, or the tablet's OEM lists how they implement charging via USB3. In order for anyone to attempt to answer, the make/model numbers for the hub and tablet would be required; however, unless this is covered in the product manuals, it's unlikely a definitive answer would be possible. Ohm's Law always applies [V[olts]*A[mps] = W[atts]] and the tablet could be summing wattage from multiple power circuits for charging.
    – JW0914
    Commented Jul 9, 2022 at 14:54

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One thing to note is that the current drawn by some charging systems is dependent on a "handshake" with the USB port -- e.g., a 1.5kΩ pull-up resistor, It could be that the PC USB port correctly signals to use a lower current limit, but that signal is not passed thought the hub.

Without knowing the specific details of the PC USB port and of the hub, and perhaps the schematic diagram of each, it would be difficult to be more specific. Could the higher draw damage the PC? Perhaps, or perhaps not immediately.

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