My main reference is "New York's Forgotten Substations - The Power Behind the Subway" by Christopher Payne, published in 2002
On page 32, there is a simple diagram map showing the substations of the Manhattan Railway and lines showing where the elevated lines were. The line furthest to the left of the diagram would be the Ninth Av El and it shows substation #3 at West 53rd St which is also near where the Sixth Av El swung west along 53rd St to join the Ninth Av El to continue northward .
There isn't mush available that I have been able to find to give any specific detail on most of the Manhattan Elevated substations (other than where they were and if the buildings are still there). I have done a google search on "Manhattan Elevated Railway substations" or "Manhattan Railway substations" and the results tend to be more general or if they are specific they deal with other substations of the Els rather than #3. You might want to contact the NY Transit Museum and ask them if they have any more detailed information in their archives on the substations of the El system.
As for the West Side Freight Line (a portion of what is now the HighLine) ran mostly on 10th & 11th Avs and was powered by (I am guessing here) by first by steam driven locomotives and later by diesel engines. According to a Wiki article there was a short section of the frieght line that was electrified used either 3rd Rail or overhead catenary because diesel engines were not permitted on Penn Station's tunnels. Penn RR had their own power station at 242 W31St (the building is still there although pretty much abandoned) to provide power for that short section of track thru Penn Station.
West Side Line:
https://en.wikipedia.org/wiki/West_Side_Line
Penn RR power station:
https://untappedcities.com/2021/01/25/p ... wer-plant/