It would have likely helped if the test also included a measurement of DC blocking. That could possibly be one area where the unit may appear to help some of the proponents of it.
Possibly but PSAudio does not mention anything about DC on your mains in their sales jargon. What they actually claim it does do is shown to be false, which us engineers already knew because we know how these things work. Their big claim is "filtering noise" to improve the performance of your audio gear yet there is zero evidence to back this claim up, nothing plugged into the P12 shows a lower noise floor at output vs not plugged into it. Of course we knew this before testing because nothing can do this between the wall and your amp. The vast majority of noise and distortion is actually created by the amplifier/device well beyond the mains cable, it's called the rectifier. You could have a perfect transmission of power, just a pure 60Hz sine wave with distortion and noise -180db. The claim is this improves your amplifier yet the instant it hits the rectifier under load you end up with a ton of noise, RF bursts, and distortion, this is where we put the most amount of care into filtering and regulation because doing it before would be pointless. FCC actually requires filters on the mains side of the rectifiers so that the nonlinear load of rectification doesn't pollute the grid. So long as the DC is clean and constant that feeds the active circuitry is all that is required for good performance and this is directly observed by looking at the output of the device.
There are two main takeaways that the subjective arguing people need to educate themselves on. One is the fact that engineers know intimately how amplifiers function because that's what we do, we engineer equipment for you to enjoy. So when we say there is absolutely no possible way a power cable or "conditioner" can do what they claim they do you should listen. If we say subjective anything should be dismissed you should trust us. Secondly, all of you subjective arguers are in denial how perception works. Humans do not passively process data from the physical world around them, we actually construct our own reality from a very small percentage of actual real data from the physical world. Have none of you seen optical or auditory illusions? Once you accept the second part as fact then the first part becomes easier to accept. Your subjective "experience" is an internal one, a construct of your own perception and nothing that is actually occurring in the physical world.
The largest disconnect is the fact people believe they are precision measurement devices that accurately and passively process 100% of the data, and can recall it perfectly at will.