My need was a tablet mount suitable for my current android tablet but also for (almost) any future type of tablets.
(tested also with an iPad Mini)

The design was made with DesignSpark Mechanical 2.0.
Construction files are attached for further development.

Due to the design the hight can be adjusted and any tablet with a thickness under 11mm will fit.
A wide cut-out in the lower part can be used for power supply.

If you drill the hole for the power cable left or right of the vertical part of the upper part you can easily run the power cable.
In my case I had to cut off a piece of the upper part to route the cable - typical case of drilling faster than thinking :)