More and more trains and planes now have plugs or USB charging ports so you can plug in your devices for charging while you travel.  On some, you may find an actual USB plug, while on others you may need an actual Electric Plug Adaptor and then a second plug that has USB ports on it so you can then plug in your USB Cable.

Think about the cable length for the use.  On a plane or train, we have found that cables of about 3 feet in length work great.  As you typically plug them into the seat back in front of you, or under your seat on some trains, the cable needs to be long enough for you to easily place your phone on your tray or front table, or to hold your phone in front of you.

In your hotel room, a 3 foot cable seems to also be a good length for plugging it in and placing it on a room table or night stand by your bed.

If you are connecting devices together such as your phone to a backup battery, then a 3 foot cable is probably much longer than what you need.  Having a cable that is only about 1 foot in length may be better.