How clean is the 5V USB out ?
Measurements are differential. One should realize that voltages below -55dB do not even get rectified by the always present rectifier and also are not not high enough in frequency (and above all power level) to even create the smallest change of DC level.
It's a good thing these devices are measured but it is important to realize the plots shown are from the actual mains (in Amir's house) and do not have any relation to similar plots of audio devices connected to mains.
Pulse spikes on mains can reach thousands of volts and will be 'clamped' which could reduce 'ticks' that can make it in the audio path when devices switch on or off.
For this you don't need to fork out $ 300.- though and many devices have these 'voltage clampers' on board to protect the electronics in SMPS anyway.
This is what's inside:
A filter and a (5V) power supply. Also looks like the connectors on the side of the device appear to connect the grounds to safety ground.
There also seems to be a DC removal capacitor inside.
Tie wrapping non filtered and filtered AC cables together and letting them run in parallel is something no EMC engineer would ever contemplate or do. Yet it seems to be done here. Above 1MHz or so the filter action will be greatly diminished because of this rooky mistake.