I plugged a cellphone into my front-panel USB connector and it started charging (without any error message) so I assume this means that the connection itself is OK, but as Krakman pointed out earlier, my iPad may require more power than the USB-3 card can handle.
The
USB-C to USB-B cable (USB 3.1) I've used is from Startech. I can't find any info about current limitations on their website. Where was there a mention of 2.5W on that Dell cable link?
It would be interesting to connect a USB-C cable directly to the USB-3 card and see what comes out of it...
PS: I don't know if this is of significance or not, but after fully charging (100%) my iPad Mini I attached it to the USB-3 card and it showed the usual "green battery with lightning" icon. I tried attaching/removing the USB cable several times and it worked the same way every time.
So next I tried draining its battery a bit (by playing a movie a few minutes, until it reached 98% battery) and attached it via the USB cable again, but this time I got the usual "Not charging" message.
So is this typical behaviour of an iPad not receiving enough power from its charger? (on second thought I should probably post this question in one of the forum's iPad sections).