Class D Technology

Power supply is no less important with class D than with other amps.   A lot of vendors focus on optimizing it and it is a common theme among better reviewed and received designs. 

Atmasphere why does 200khz bandwidth matter if there are no sources practically (record or CD res digital) that can even come close to delivering it today?

I did explain this in my post but here it is again:

In order to reproduce phase correctly bandwidth is a requirement. Put another way, if the bandwidth is not there phase shift is the result. You are correct that digital doesn't have bandwidth and that is one of the reasons that the LP sounds better and is still around after all these years of being 'obsolete'. Nevertheless, to prevent phase shift in the amp you need bandwidth even it its not there in the recording. In fact the recording doesn't matter.

To put this another way: phase shift components can be heard to 1/10th of the cutoff frequency. So if you are cutting off at 20KHz there will be phase shift to 2 Khz. 100KHz cutoff means that phase shift will exist down to 10KHz. We older adults don't hear so well at 10KHz so you can sort of get by with 100KHz bandwidth but if you really want to do it right you better have 200KHz so your kids will like the stereo (unless you're the type that just wants them off your lawn...).

What prominence does the heft of the power supply play in the sonic performance of Class D amps relative to SS or tube amps?

The supply should be clean else IMD components related to the noise in the supply and the scan frequency will show up in the output. IMD is pretty audible to the human ear (shows up as brightness and grit or 'grundge'). Since the scan frequency is pretty high the power supply had better be properly bypassed to be effective at the scan frequency! But it can't have any sawtooth going on either. Otherwise the supply has to be able to support the operation of the amp at full power, even though most of the time the supply will see a fraction of the current draw that a traditional amplifier supply would see, so most of the time the power draw from the wall is minimal.

Traditional power supply design or SMPS is irrelevant so long as the supply is quiet (SMPSs have the advantage of being easier to regulate...).

Assuming nothing is there to start with isn't a phase shift of 0 = 0?

I did not know vinyl has frequency bandwidth so high.    Most home hifi always talked of 20-20K frequency response.     Is this in practice or theoretical?   I'd agree theoretically vinyl could do more but practically its news to me.   The best digital (higher res) sounds as good as most vinyl to me these days.    RTR is better but look where that got us practically.

Also what is the math relationship between bandwidth and phase shift? Where does 10X bandwith number come from? is there something akin to Nyquist that is used to determine this? Did the engineers making high end Class D amps miss the boat on this somehow? it does not sound like they did in practice based on listening, at least the good ones seem to know what they are doing.

From my perspective there is understanding the theory which is useful and how things sound, for which there is no mathematical equation to properly represent that. Pundits focus on the strengths of a supporting theory and skeptics the weaknesses. No approach is perfect and holds all the cards. That’s clear by the variety of successful amplifier designs out there today.

Ralph sounds like you are actively prototyping your own class D designs? that tells me you think there is in fact something worthwhile there if done right.

Dear Audio Friends,
I write this as one who is rather un-technical but possessing excellent 'ears'.;-)
As one of the few who have all 3 main amp designs in house and active in-system, and who owns 6 pair of priastine and extremely detailed Apogees, including a purely1 ohm Scintilla pair completely rebuilt by Rich Murry of True Sound Works, I am making a rare post here to clarify a couple of things re my experience with amps of all persuasions:
In my room as I write this I have 2 of Henry Ho's H2O SE amps driving my Scintillas, and the staging, imaging, frequency response and range are world class. I gave up a pair of beloved Class A Nelson Pass XA100.5s for them, as I could tell very little difference whiule getting some serious power benefits for my room and speakers. Please note that Henry Ho first made his name as a successful and well-reviewed Class A amp builder, and his Class D amps have Class A grade power supplies. They weigh 60lbs each, and mine have some extra-fine caps, to boot.
I also have a pair of custom Bob Carver built-for-me-by-Bob-Himself KT120 tube amps that he designed specifically to drive 1 ohm Scintillas. They have a 1 ohm tap, and sound exquisite, with a slight wider stage and image than the H2Os, but not as tight a control over the transducers, of course. These are NOT like my Kronzillas which, though superb and with unrivalled detail and finesse on my other Apogees, can NOT drive a 1 ohm Scintilla - nor would I ever try!
I have other amps, hybrid Vincents, Wyred4S SX500s, a fine Class A Coda 3.2 Stage, and the H2O and Carvers out-do them all by a wide margin in every particular.The only exceptions at all are the T1610-tubed Kronzilla DX MkII monos.

I hope my personal and ongoing experience with these amps might lend a bit of boots-on-the-ground substance to an otherwise thorny and subjective discussion.

My final and main point, really is this: From my experience it seems - and I have discussed this in detail with both Bob and Henry - that each style and design philosophy has its strengths and weaknesses: HOWEVER, as the designs and designers progress to the pinnacle of what is possible to each, the differences become a matter of diminishing returns. They each become less distinguishable in a blind test, with almost equally transparent and less 'visible' between listener and music.

That is and has been my experience.
All the Best