Below in the photo both SMPS power supplies powers some DAQ boards. I named them as 12V PSU1 and 5V PSU2. As you see the PSU1 and PSU2 are daisy chained at their mains entry(line, neutral, earth):
And here is the basic diagram:
Above both power supplies powers the different parts of the remote device Device 1. In real there are six of them but or simplicity I draw one device. The PSU1 directly powers the device, the PSU2 powers the 5V part of the device through a USB Hub.
I named the nodes as A, B, C, D and E.
Knowing that in SMPS A E and C D nodes are capacitively coupled, is there a loop for high frequency across A B C D and E?
If there is can I eliminate that by cutting the daisy chain earth between D and E?
Block diagrams of the power supplies:
And here is the power line filter.