I have been totally uninformed about private rail cars and am enjoying learning about them. At our long stop in Sacramento I talked with the "Conductor" (at least that's what the lettering on the badge of his hat said) of the private cars we picked up in Portland. He runs a business of setting up train trips for pricate car owners, which can be a day or days long. Some cars are owned by one person, some by a group, and they pay a rental fee to "park" on some track in some rail yard. Then they request (and pay a fee) to hook up with Amtrak on a line that is going where they would like to go. There is, of course, a club for these folks, and a magazine called "Private Vintage", named for the cars that were once made of (highly polished) wood.
To use Amgrak, the cars must be kept up to "code" for electric, water, etc. by standards set by Amtrak. Once up to standards there is the maintenance and repairs of old rail cars to keep up with. The first car on our train has, by request of the owner, been transformed from a pullman sleeper car to a party car with bandstand, live music, bar and dance floor.Unfortunately I could not get a photo of the cars. My walk in Sacramento took me by them in the dark, and they were dropped off in the yard at Oakland before we could get off for a walk.