I had about the same experience adding a buff n blend on an aion board (polaris), lots of trials before getting it to work.
That one does not have the trimmer... so I'll let others more experienced explain it. My first thought is it's function is to set the level (volume) of the signal sent to...
I think the trimmer is there to set the wet volume to your liking, depending on your preferred settings on the fractal. But the buffer could affect the sent signal maybe? How about phase inversion ?
I think the power jack connections goes to the center of the aion daughter board. Then after power protection it goes out to the board at the left. If you feed 9v on the left connection, the reverse diode will stop the current.
Have you tried to unbox it and see if signal goes through ? Electrical tape will get punctured by you cut leads, specially when thightening the pot to the enclosure, it's no good, you are better off with a piece of cardboard.
Here is the drill template I used for mine. Fell free to use.
Robert told me that if you use a 5mm Male standoff paired with a 20mm Female standoff (on opposite sides of the PCB) you don't need any mounting holes or hardware on the outside of the enclosure...
If you like how that one turned out, I could share it.
Thread 'A powerful trio' https://forum.pedalpcb.com/threads/a-powerful-trio.21563/
Edit : you can now find it here
https://forum.pedalpcb.com/threads/usb-power.28655/
The 3 holes are to accomodate different lead spacing for electro or film caps.
With tantalum, polarity must be correct so the + hole is important, my guess is that the 2 others are connected together, so yes outer ones are correct.
Using the TEC 3-0922 would do it
Edit, as @jwin615 pointed out, the 3-1222 if you want to use a 9-18v power supply.
Is there is a voltage regulator before the traco ? What circuit is it ?
I'll admin it's weird that lifting ground makes it working ...
Yes, that means those 3 portions of the IC are not connected or not in use (like using only half on a dual opamp.)