Somewhere in Japan there is a guy who was so fixated on reducing his AC line noise in his stereo system that he had a new power pole and dedicated transformer installed at his own expense. That's sort of extreme, especially since there seems to be so few quantifiable ways to measure line noise, and even fewer ways to figure out if A. It is a sonically-detectable problem, and B. Whether your solution to the problem really is doing anything positive.
First, a brief history of AC line noise and audiophiles. Enid Lumley was the first audio writer to mention that her system sounded better late at night. She postulated that it was a function of AC line noise polluting her power. Others agreed, and soon there was a sub-industry within high-performance audio creating devices to reduce or eliminate AC line noise.
As to whether any of these devices were effective is debatable since there really is no way that I know of, besides subjective listening, to determine if the sound is better or worse with added AC devices. Sure, there are some test devices to measure AC noise on an AC line, such as the Noise Sniffer and Monster Entec measuring box, but the problem is even when it is clear that these devices show that an AC filter or conditioner is letting less noise through, there's no way to corollate whether that noise reduction is having a positive effect on the overall sound of a system.
Recently I received a new AC power conditioner device from IFI, called the Power Station. I measured it with the Entec and Noise Sniffer. In both cases they showed no reduction in AC noise whatsoever.
Does that mean the IFI device is junk? Not necessarily. It could be the IFI's filters are above or below the frequency range of the measuring devices. Or it could be the IFI device is doing nothing or doing something that will only be noticeable through subjective listening. An interesting side note was when I plugged in an Audio Prism Quiet Line parallel power line filter into the IFI device the noise level as measured by my two test devices dropped to almost nothing...
I have and use power line devices that when tested did reduce the AC noise as measured by my test devices. But to be perfectly honest I've never noticed a vast or even a consistently noticeable improvement in overall sound when a system was routed through them, but since they also supply protection for my system from AC weirdness, I use them.
The issue for me is that even with a positive result from my test devices there is no consistently quantifiable way to tell if AC noise reduction is actually making a system sound better, besides listening and making a subjective conclusion based on that listening.
While I do not dispute that AC power is fraught with noise issues that can affect the performance of a stereo system as well as other electronics, it's too bad that after all this time no manufacturer has come up with a device that can both measure and correct for AC line issues in a quantifiable and repeatable way. The component that has come the closest to this ideal is the PS Audio Power Plant 12, which supplies several measurements that show what it is doing to the AC signal.
And while this does graphically demonstrate that a better signal is coming out than went in, it does not indicate whether the results will be something you can hear...for that there is only current remedy - to listen for yourself and see if you notice an improvement...which may not be sufficient motivation for acquisition of such a device by audiophiles with objectivist tendencies...