John's probably seen this but  I think it addresses power on cables and branching nodes (which are just optical /roadm devices)

https://youtu.be/H9R4tznCNB0


On Thu, Mar 17, 2022, 22:40 John Levine <johnl@iecc.com> wrote:
It appears that Jerry Cloe <jerry@jtcloe.net> said:
>-=-=-=-=-=-
>
>it look like it was completely at sea, but it would kind of make sense
>to leave them at sea if you could put a router there.
>
>First thing that comes to mind is power, how would you power them?

Undersea cables have had power for repeaters since TAT-1 in 1956.  I
think we can consider that to be a solved problem.

R's,
John