The Plasmatron - more linear output voltage

Negative differential resistance would be the better term, since it has to have some resistance in order to produce negative resistance change. Fluorescent tubes are also a negative resistance devices.

I cannot see how this device would help with gear that already has built in voltage regulators - pretty much any device other than power amps, but today many power amps have SMPS including half of class D amps and some class AB amps like the newest high power amps from Rowland. Perhaps resistance of this device have some filtering effect reducing power line noise.

"My friend has specifically mentioned Krell as a company that uses scientifically correct and sound marketing where a EE can truly appreciate something g about the equipment."

Your friend might want to re-think that one. If there's one thing we know about Krell's marketing, its the slogan "un-phased by any load". They built their business on that phrase. The problem is that its a flat out lie. There's no amp that's un-phased by any load. If that were true, they wouldn't be making amps that put out different amounts of power. Based on their marketing claims, there would be no need to.

Krell is still hanging on to that idea that tube preamps produce DC at their outputs, which is absurd. Not impressed.