Re: Will a HTC one x case fit all HTC phones?
Only One X and One X+ have the same dimensions. The newer versions M7, M8, M9 all have different designs. though M8 and M9 look similar, they have slightly different design.
Re: Galaxy S6 doesn't charge and says "dock is connected" when I unplug the charging cable
Did you try using a normal 5V 1A usb charger instead of the fast charger?
I use my old OTG cable which I used with my previous HTC One X, and it works like a charm. USB pendrives, WD passport.. everything works fine and the data transfer rates are better than my HTC.