This is a recent topic:
Open the wall warts and have a look at the absolute crap they use inside. They are mostly a transformer, with a couple dirt cheap diodes and an even cheaper cap. Usually on some POC circuit board. So for like $10, maybe $20 tops, you replace the crap with quality diodes and caps. Then for bonus points you solder it back together point to point with actual wire, eliminating the thing circuit board trace altogether.
This makes a huge improvement. Takes up almost no extra space. Guaranteed to perform better than any power supply under $500, and for peanuts.
The Synergistic Research Active Shielding wall warts in my system are modified this way. Huge improvement. https://systems.audiogon.com/systems/8367
The reason you see no wall warts is after doing the mods they are all hard wired to power and mounted inside the conditioner.
I have MCUR LDA linear power supply for my Clearaudio turntable you could see the difference on the the strobe disc with the wallwart the speed fluctuated ever so slightly with the linear its rock steady I have the upgraded one cost was about $425 the regular one is around $230 they are different amounts depending on application
It's the transformers in the switching power supply wall warts that make them noisy,... not so much the diodes and caps. Linear power supplies can definitely be noisier than switching supplies as LPS use larger transformers which contribute to magnetic interference and hence AC hum. The key is to use switching supplies with small but high-powered transformers that can keep produced magnetic fields in check. You're looking at it all wrong just comparing an LPS to a switching supply - it's the transformer/isolation design that makes a difference IMO - and not some cheap diode or cap.
@mkgus - the Teradak and Zerozone linear power supplies that have two outputs are actually two separate power supplies. I have seen some that share a single transformer, but have two independent power supply boards. I have also seen some Zerozone that actually have multiple fully independent transformers and power supplies within a single case/unit.