Here is a round of tests using the Arcam rHead Headphone amplifier. Its stock switching power supply is 12 volt so I used the fixed 12 volt out of HDPlex 200W for testing.
First, the dashboard with unity gain with its own power supply:
View attachment 27150
And now with HDPlex 200W:
View attachment 27151
There is absolutely no difference.
Let's measure signal to noise ratio at 50 millivolts:
View attachment 27152
Again identical so no improvement in noise floor, black backgrounds, etc.
Finally 1 kHz FFT with wide bandwidth:
View attachment 27153
There is a tiny differential above 50 kHz but totally inconsequential.