Simplest Linear PSU?

Regulation done right typically reduces noise. Done wrong or badly or with defective parts, I suppose it could add noise. Even for a home built LPS, there are excellent prefabricated regulators available as add on devices. Most important is to plan ahead for voltage and current needs and to account in advance for the headroom that any regulator needs.

Regulation done right reduces noise on the supply, rather than adding noise.

Building a good LPS is or can be a little more complex than implied. It helps to have an oscilloscope to analyze the performance, too. Learn about pi filters, etc.Also, you may want to regulate the V output in which case you design for a higher V output than needed to allow headroom for the regulator to operate. 

Although I definitely do not agree that SMD are categorically to be avoided at all costs, nevertheless it occurred to me that for those obsessed with avoiding SMDs, I would go along with a recommendation I think made by someone else to look on Ebay for laboratory grade DC power supplies. Those made by lambda or by Pharmacia, for two examples, are of very high quality well regulated and permit adjustment of voltage and current. However they are also relatively large in size, and some have fans for cooling that will make a tiny bit of noise in your listening room. They are meant for laboratory use, for real. And most likely anything you can find these days will contain semi conductors. Heaven for bid!

Charles, like Mijo, I’ve never had occasion to shop outboard power supplies of any type.

I think the reason many people report audible benefits from LPSs vs SMPSs is that they have upgraded from a wall wart quality (i.e., low quality) SMPS to a high quality LPS designed for audio. David Berning has been implementing SMPS power supplies in his state of the art amplifiers and preamplifiers for years, if not decades, and no one seems to notice. If it’s done well and well built, an SMPS can certainly hang with an LPS. And the benefit is you won’t get a hernia from lifting an SMPS-powered piece of gear.

Where are your data that show “most audiophiles prefer simple circuits”? Most have no clue regarding circuit design. In certain applications, SMD have some advantages, such as reducing stray inductance and capacitance that can arise because of longer lead length and layout of through hole parts. Also, are you looking for tube rectified PSs? Because SS rectifiers can be construed to be semiconductors. Finally most commercially available LPSs are going to use semiconductors for regulating the V output, unless you want unregulated.