Review here: https://www.audiosciencereview.com/forum/index.php?threads/puritan-audio-psm156-review-ac-filter.26136/
Conclusions: As you see, I have run a number of tests to give the PSM156 ample opportunity to show it can do something to improve audio but it can't even move the dial one hair. There is no indication or logic that would tell us that it can make an audible improvement. Yet the company says this in the feature list of this product:
* 52 cumulative stages of purification removes common and differential mode interference, enhancing clarity, staging and dynamics.
* Equal resistance routing to all outputs realises full dynamic performance.
* Integral earth management system inbuilt with cleansed ground and star earthing format further lowers the noiseNone of these things is observed in the measurements.
The device however seems to have real filtering in there as opposed to toy implementation we see in other audio devices. So if you have audible mains related interference that is above a few hundred Hertz, then the PSM156 may have an effect.
As an audio fidelity improvement device, I can't recommend the Puritan Audio PSM156. As a mains filter in general, it seems to be well built and does a far better job than typical consumer gear sold for this purpose.