As well as slip rings being an option, you could also use a commutator.
When I made a large globe, I found it easier to source commutators from DC motors than slip rings. You can get them in all shapes and sizes.
Make sure to get one with at least 4 phases. The one I got had 12 so I joined adjacent phases together to form 4 groups of 3. Then, in order to prevent shorting or dead time in the supply, you use a 4 phase bridge rectifier.
That allows for a smooth DC supply without gaps or shorts that would normally happen during commutation.
What I also did was to use a higher voltage supply and then build a switching regulator on the globe arm. This reduces losses from the commutation and with plenty of capacitance gives a nice smooth output. I went with 24V as the supply switched down to 5V.
You can also feed mains AC on to the brushes and you'll get rectified DC on the arm. You can then get some nice high voltage DC-DC converter modules to step it down. However I would advise against using mains AC directly - much too dangerous. I'd get something like a 24V power supply brick (of 48V), both are considered safe low voltage.