I am using a Midi Solutions Merger. It only powers from the H9 if you have an closed midi loop. If you connect the output of the Quadra Thru to the input of the H9 and the input of the Quadra Thru to the output of the H9 you wil see the light of the Thru lit. I’ll guess it is a midi ground thing. The H9 probably has special wiring (midi ground not connected on output connector?). The loop described does not help because it is useless, but in my setup, which has a closed midi loop it is working perfectly. See the picture below how my midi is setup on my pedalboard.
The mi.1 is a wireless Bluetooth LE adapter so I can control both my H9’s by bluetooth from apps on my ipad. This works great and the merger draws the power from the H9 output thru the mi.1. Maybe you can create a closed loop too? Otherwise you probably need an extra MIDI Solutions MIDI Power block. If the picture of my midi setup is not showing up, I have attached it too.