You typically will need one high-powered (5W) USB port for each of such devices to charge efficiently. The iPad alone requires more to charge, hence the non-standard 10W adapter. In addition, the USB hub itself is not likely to provide the necessary wattage to any of the ports (these usually are low-powered ports), so chances are not even one device will efficiently charge when connected alone to such a hub.
Yes it is possible, but consider the consumption and Costs.
How much electricity does it take to power your iPhone for a year?
The answer: 1 kWh.
This is the amount of electricity you’d need to power ten 100-watt incandescent light-bulbs for an hour.
Far from anything worth being sheepish over, 1 kwh costs about 12 cents.
To be specific, your iPhone battery holds a charge of 1,440 mAh, or about 5.45 watt hours. If you fully drained and recharged your phone everyday, then over the course of a year you would have to feed it about 2,000 watt hours, or 2kWh = 25 Cents per Year.
As for your iPad, keeping it fed costs just $1.36 a year, according to the Electric Power Research Institute.
Your average laptop, with its far bigger screen, uses about 72 kWh, costing some $8 a year.
There is your challenge:
Make a power station that has a ROI such to recover the cost using the 25 cents per Year returns.
Answer: if it cost you $20 to make the power station- it will take about 40 Years before you see benefit.
Best Answer
This answer is indented to be canonical answer for similar questions and applies to all devices that utilize USB (Type A or C) chargers and conform to the USB Power Delivery specification (version 2.x through 3.x).
Yes, it can be used and you will not cause any damage.
USB-C conforms to the USB 3.1 specification. Part of that specification is the Power Delivery spec. This means that the device and charger will negotiate the power that is delivered.
As to whether a charger is too powerful or not, you can always use a charger greater than or equal to the maximum power draw of the device. This applies to all chargers (USB, barrel connector, etc.), not just those that conform to the USB 3.x specification.
In other words, if your Apple USB-C charger is capable of delivering 87W of power, but you only need 10W for your phone, you can charge your phone no problem.
However, your 10W phone charger should not be used to charge your 87W MacBook. Why?
(MagSafe power adapters have a chip built into it prevent using an under-powered charger).
Possibly. The power delivery spec allows for power negotiation. If there is sufficient power, it will charge, albeit slowly. It may charge, but not power your device. It may do nothing (it couldn't agree on a negotiated power delivery so it stopped delivering power). If it's a poor quality charger (and does not conform to USB 3.0+ spec) it may overheat.
This is why you always use chargers greater than or equal to your device load.