12v linear power supply

It is much more than just blocking A/C noise. It is how smooth and powerful the current is. One analogy I use is to use air compressors as a comparison to switching/linear power supplies.

Actually, no, its the noise. And i'm not sure what you man by AC noise, the noise is (by definition) AC superimposed on DC and is a product of the way Switching mode power supplies work. ( i wont go into that here, look it up)

Don’t use analogies, define your terms and explain the engineering.

Switch mode power supplies create a lot of high frequency noise - its well known, its a problem too. It can interfere with the digital circuit by making tiny adjustments to the zero crossing (we call that jitter) and it can beat down into the analog region (we call that non harmonically related distortion).

I design this stuff. Its the noise. and its a problem.

Actually, no, its the noise. And i'm not sure what you man by AC noise, the noise is (by definition) AC superimposed on DC and is a product of the way Switching mode power supplies work. ( i wont go into that here, look it up)

Yes, I know how switching power supplies work.  They use very small capacitors and a small transformer.  Then use a circuit that injects DC charges onto the post transformer caps thousands or tens of thousands of times per second.  This is different  than linear power supply which charges the main power caps about 60 times per second (or 120 depending on how you look at it).

I have done work with both switching power supplies and linear power supplies.  The switching power supplies suffer from weak bass because of the small caps and transformer.  The only way to get a switching power supply to really "act" like a linear power supply is to place a very large amount of capacitance after the transformer/charging circuit.  Let your ears be the judge.  The lab measurement devices don't tell the whole story.

Don’t use analogies, define your terms and explain the engineering. Switch mode power supplies create a lot of high frequency noise - its well known, its a problem too.

Funny coming from someone claiming to be an engineer.  You claim you want rigor and then immediately come out with broad, general brushstrokes.

A well designed SMPS can have extremely low output impedance and noise, far lower noise than a LPS, if well designed.

It's a lot easier to design a low noise SMPS than a low noise Class D amplifier so a lot of the problems associated with Class D are easier to deal with in a power supply.  Unlike a Class D amp which has to output AC, for instance, an SMPS only has to put out 1 constant voltage.