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.
Favorite Linear power supply
I have a couple of walwart power supplies in my system which I’d like to replace with a linear supply. It’s mostly computer related such as my router, etc ( I have a Belkin). Can anyone recommend a good choice(s) at a reasonable price point ( under $200 or so?) preferably one unit which could accommodate at least 2 items, as above. I don’t have a tremendous amount of space behind my rack but if it’s not especially big I’ll be able to find it a spot. Thanks in advance.