Hi,

To answer your questions:

I usually power the system using MeanWell GST25A05 5V 4A power supply.

1) When I plug the power supply into X820 and RPi is powered from X820 via 2-PIN power cable (and also connected via USB of course) - reboot does not work.

2) When I plug the power supply (the same MeanWell) into RPi and X820 gets the power only from RPi via USB (2-PIN power cable is not used) - reboot works fine. However, there are 2 problems with this configuration

   i)  power button on X820 does not work
   ii) RPi periodically reports an undervoltage warning (hwmon hwmon1: Undervoltage detected). This does not happen when I use a different SATA to USB dongle instead of X820 or when I power the system via X820.

Please let me know if you want me to run an additional experiment