Anyone with experience bringing mobility scooter on Amtrak?
Yes, I've been on sleepers and Amfleet coach (Silver Service). I have a 3-wheel travel size scooter, Pride Go Go Elite Traveler.
At low-level platforms, you'll be cranked up on a manually operated portable lift. You can drive onto and off of the lift and remain seated; but it can be difficult to maneuver around the corner into the car. I found it easier to get off, release the brake, and roll it in (but I've had a lot of experience rolling scooters, having been a Disney bus driver

).
On sleepers, you'll want to reserve the accessible bedroom, which is right next to the entrance on Viewliners, and straight down the hall on the lower level of Superliners, so there are no additional turns to make once you make it into the car. There is room for the scooter, but you may have to move it around to get around the room.
On coaches, my scooter is not stable enough to ride on a moving vehicle, so I need to transfer to a seat. By default, Amtrak expects you to stay on it. So if you want to transfer, you need to call and reserve both the wheelchair space and the companion seat. You cannot do this on the website or app. They told me it's better to call in the first place rather than make an online reservation and then try to modify it. There was no additional charge for the companion seat.
Just a note: on both coach trips, I was riding backwards in the companion seat. This might vary depending on how they assemble the train.
I'll be happy to answer any questions.