I didn't come to any solution working with this ext. powered hub. The Tablet didn't charge and run the ELAD FDM-S2 at one time. Following a tip I cut the ground line of the mini-USB-connector, but this didn't work either. It's reconnected again. I tried to connect 470 Ohm resistors in both data cables of the connector. (As described in
Perseus_SDR Group)

According to the Perseus_SDR Group link the resistor should be set only between line A und B, but this does not work with the Tablet either. Connecting 124 kOhm and 36,5 k Ohm resistors (from: ... searchtips) in the same way did not work either. May be it's all bullshit.
At this time I dont see any chance to charge and run the ELAD FDM-S2 in parallel with this Trekstor Surftab wintron 7.0.