When it comes to traveling via rail, being aware of specific railway requirements is extremely important.
Amtrak allows passengers who need to use any kind of oxygen equipment (whether tanks or POCs) onboard, so long as it is for passengers with a defined disability. Any passengers planning on using oxygen equipment on an Amtrak train must make their reservations via telephone (Amtrak.com does not allow for reservations that include oxygen equipment), so call 1-800-USA-RAIL to inform the rail line in advance. (See https://www.amtrak.com/use-of-oxygen-equipment.)
All oxygen equipment taken on board any train must be able to operate WITHOUT onboard electrical power for a minimum of four (4) hours according to Amtrak (so they still function in the event of a power disruption on board). Bring as many batteries as necessary to meet this requirement when planning your trip by rail in case of emergencies.
Most domestic trains, whether regional, local or commuter rail lines, usually follow similar guidelines to Amtrak, depending on the length of your travel. International rail lines may have different requirements as well as different outlet needs, so be sure to check with specific rail carriers before traveling to make sure any and all guidelines are accommodated.