One of the many Youtube channels I subscribe to is a Swiss train driver
who records the journey from the driver's point-of-view with a GoPro
mounted to the windscreen. Last week he posted a video of the Zürich
Uetlibergbahn, which is notable in that it is one of the few railways
in the world that routinely operate using two incompatible power supply
systems on the same track. The Uetlibergbahn itself is electrified at
1200 V=, and for a few kilometres between Zürich Hauptbahnhof and the
junction with the Sihltahlbahn the line has the standard Swiss 15 kV ~
16.7 Hz system. In order to run both systems simultaneously, the
Uetlibergbahn uses an overhead wire offset to the side, and has done
for the last few decades without issue (though plans are afoot to
gradually convert it to the standard system in the next few years).

https://www.youtube.com/watch?v=Ma-ZwzM_LUk (going up)
https://www.youtube.com/watch?v=nYtuVfkCw_g (coming back down)

What's even more remarkable is that these two lines run 4–6 trains each
per hour per direction (12 per hour per direction in peak), and the
only double track section has the constraint that trains on each system
can only pass at one place (Uetliberg trains between the terminus and
the next station, and Sihltahl trains between the second and third
stations). Someone should take a manager from Metro or Sydney Trains on
a tour of Zürich and show them how it's done (the signalling and
timetabling, not the engineering oddity!).