Hi, Werner

I have tested two Y-cables Xiangfu bought:


They both have the ID pin connected to GND in USB Micro B port as the OTG host.

The first one should meet all the needs:
Works fine when connecting usb keyboard/mouse/disk on the OTG slave (the standard USB A female)
The power branch does deliver power to both slave and host, only failing in charging a Nexus5. But it can charge a Nexus4 and power up a RaspberryPi.

One problem is that the power branch has a Micro B female and is not long enough. But we can connect it with a Micro B male to Standard A male cable which is very easy to get:

The second one has a chip inside.
It cannot work properly when all three ends are in use.

Another cable Xiangfu ordered should arrive in a few days. I will test it later.