Toroidal vs SMPS for Class D Modules

It's possible for small measured differences in two devices to not be audible, or just barely so. Both the xfmr and the SMPS can work equally well. Pros & cons would be price, complexity and weight of the selected device. Xfmr is simple in design, very reliable, generates little if any HF hash, (diode reverse recovery, maybe) but is heavy, and has limited voltage regulation characteristics. SMPS get you light weight, voltage regulation, but HF hash and reduced reliability since it has more parts in it that could fail. As for sonics, if the DC is clean and steady, the choice does not matter.

I specialized in car audio mechatronics for several years in the heyday of car audio class AB amps and the DC-DC conversion was done veryyy well. I repaired small and very large monster amps and had no issues with PWM DC power supply purity.

Most SWPS I have encountered do have voltage regulation. Something in the design of the supply has to control On time of the switch to get a desired DCV at the output terminals.

For audio power amplifiers, using a regulated SMPS is not without issues.
To quote @Armand:

Regulated SMPS'es that try to keep the voltage constant on the output (by using feedback) can introduce modulated noise on the power rails if the feedback control loop is not fast enough (which it typically not is.)
The perfect power supply is of course one that keeps the rail voltages 100% constant regardless of how many amps drawn with a bandwith of at least 20kHz, but that would be very expensive and not really pay off. Especially not on todays class D amplifiers with a lot of feedback that just corrects everything anyway.. On power amplifiers without feedback it is a totally different story.

A toroidal or transformer based power supply will be near bullet proof, and more reliable. A typical 500va toroidal transformer weighs around 11 pounds and will not necessarily be bulky or add to much weight so to speak. It will of course increase the cost to produce for manufacturers, who can spit out an entire SMPS amplifier case and all, for less then the oem bulk cost of buying hundreds of transformers. It will also increase the cost to ship. SMPS is 10 fold more profitable for manufacturers at the minimum.

500 va would be more then enough to power the new hypex modules. Such a transformer would easily be capable of peaks of 500 watt PER CHANNEL. Given this the major excuse not to use them is that the manufacturer would be 10 times less profitable doing the same amplifier with a transformer. New tech in SMPS has always been profit driven and is the main reason why transformers have been withdrawn by manufacturers, in favor of making their own smps modules. In order to ensure you buy in on their huge profits they sell you on , efficiency, weight, cooler running etc, most of which means little to actual audio reproduction in a 500 or less watt per channel amplifier.

When transformer amplifiers were the mainstream, one would find overbuilt units, and what they referred to as underrated units. The underrated units would point to the musical nature of power, and acknowledge that one could use a smaller transformer in many cases. as it would only have to supply peaks for short durations. Classic pro amplifiers like the crest ca series implemented transformer under rating, yet were known to be among the best for long term reliability, and able to survive two ohm abuse.

When gobs and gobs of cash in this magnitude is on the line, you can be sure to hear a lot of snake oil and bs about SMPS. https://de.m.wikipedia.org/wiki/Transformator, https://www.thel-audioworld.de/module/Netzteil/Infos.htm, and other.

Depending on the design and construction, transformers can briefly deliver a multiple of their rated power. Power supply units based on this can, if designed accordingly, also briefly output higher power than the nominal power.
As far as I know, this ability is not as pronounced or non-existent in smps. I'm not saying linear power supplies are better than smps or vice versa. It always depends on the design of the power supply and the application, in this case the corresponding amplifier and its design.

For further basic knowledge, but also the translation, you are welcome to use Google, maybe Doug Self has also written something about it.

There are statements that amplifiers should also sound different depending on the power supply (for example https://www.diy-hifi-forum.eu/forum...-Vorstellung-LJM-L20-5-Amp&p=&viewfull=). I don't know to what extent this is double-blindly secured, i.e. ASR-proof. I myself form oops I can also hear differences...