Some points on power. You are right - you need to have 900 mA (0.9 A) available at each port. But the specs they publish make that tricky to figure out, so here's how.
Normally they will NOT tell you 900 mA per port all in use simultaneously, nor will they tell you 900 mA per port. What they WILL tell you typically is max TOTAL amps at one time, or even total WATTS. And that is sometimes hidden in the specs for the "Power Brick" module. And then it gets trickier yet, because although the power coming out of a USB3 port is at 5 VDC, the "Power Brick" supplied very often puts out 12 VDC to the Hub, and the Hub does some conversion. So the only way to figure this out is to work in WATTS!
Now, Watts = Volts x Amps. Further, total Watts out (from Hub ports) must be slightly less than total Watts in (from the "Power Brick" module), allowing for some efficiency loss in conversion. For example, if you have a USB3 Hub with 5 ports, and ALL of them are supplying the max 900 mA per port at 5 VDC, then it is putting out 5 x 0.9 = 4.5 W. To do that, its supplied "Power Brick" should supply more than 4.5 W - say, 5 W to be safe - at 12 VDC (IF that is the output voltage on the power module). If the module specs specify A, rather than W, 5 W at 12 VDC is 5/12 = 0.42 A, or 420 mA.
The next factor is a common feature these days on USB3 Hubs - some "Charging Ports". Although the original USB3 specs said nothing about these, they are ports that conform to certain additional standards that allow supplying much higher currents on certain ports, and can negotiate just how much more with a device designed for that. Thus you will see Hubs advertised with a FEW of its ports able to supply "up to ..." higher numbers like 2.5 A. If you examine one of those, then you need to do separate calculations for the "normal" USB3 ports and add those up for total Amps (or Watts). Then do a second calculation for the few special high-power Charging Ports, and add that to the total. THAT is what is required from the "Power Brick" supplied IF you plan to actually use those charging features.
Lastly, you will find it VERY common that the "Power Brick" supplied does NOT provide the max power the Hub's ports might be asked for by connected devices. This is becasue it is NORMAL that only SOME of the devices need the full 0.9 A specs of power from the Hub, and many do not. For example, a keyboard or a mouse uses MUCH less than the 900 mA max allowed, but a "Laptop Hard Drive" external unit needs the full 900 mA to work. So makers provide a "Power Brick" module for, perhaps, 70% of the absolute max based on port number, and assume it will work just fine in "normal" use.You can judge for yourself, based on the devices you plan to connect, whether that is going to be OK. In doing that, consider buying a Hub with more ports than you need, just to get the higher-capacity "Power Brick" that comes with the larger Hub. Also be aware that SOME Hubs with Charging Ports may NOT be suited for using normal USB3 devices on the special Charging Ports; in those cases, the Charging Ports are of no use if you cannot use them.
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