Yikes, I'm back and now will wedge myself between the arguing techs...
Steve, the reason I said 'no' to whether a power line conditioner will make any difference with an SMPS is the reason given here:
Originally Posted by lcaillo
Virtually all modern switching power supplies in video equipment full wave rectify and filter the a.c. to d.c before applying it to the switching converter. Then the switching device(s) apply the d.c. in pulses at a frequency between about 50 and 150kHz to the switching transformer. On the secondary side it is rectified, usually by a high speed fast recovery diode, and filtered. It is usually further filtered and regulated before being applied to the circuits in the set. There is often some type of feedback to the primary switching circuit that affects the switching frequency to vary the power generated by the circuit.
It makes no difference how distorted the waveform is nor how imprecise the switching points are in the original line a.c. wave because it is fully rectified before being supplied as d.c. to the switching circuits. In fact, these supplies are incredibly robust in terms of being able to deal with voltage swings and output the same voltage and current.
So I agree, since the switching part of the power supply doesn't start until AFTER the incoming AC is filtered, I don't think a solid 120 volt AC input with maybe some glitches on it (Caused by refrigerator startups, slight voltage fluctuations, etc) will affect what comes out of the SMPS. (again, we're talking real life situations and installations, not the Chevy Chase scenario of someone plugging 15,000 watts of Xmas lights that pulse on and off into the same breaker panel as your stereo, etc).
We all pretty much agree, SMPS's are VERY noisy. The switching transformer is run on square waves at 100-150Khz generally, and square waves have harmonics into the Mhz range, albeit low level harmonics. Clean AC input power won't change the noisiness of the SMPS, so again, I can't see the conditioner making a difference.
AV has already outlined how brute force non SMPS power supplies have massive filtering, so I won't repeat that here.
Steve, I will come down one day, and you'll show me how your conditioners affect your a/v system. I consider myself to have a good set of ears, so we'll see what happens..