Hey all, I am trying to get my dad's old M-track set up and running. Anyone know if there are any good options for a replacement power supply? Does it have to be a Marklin product or will others work?

Welcome to this great forum.
Märklin transformers are really the best to use a Märklin train.

On old transformers (before 1955) you may need to change the power cord (You need to be an electrician)

Avoid using these old transformers with recent Märklin digital locos as the direction change impulse may (probvably will) destroy the electronics

Avoid using pre-war Märklin transfos as they are not adapted to the "Perfekt Umschalter" (Märklin direction change system).


I opened my 280A Märklin transformer (1951 6 plugs at rear, just earlier the one shown on video) because the power cord made of rubber was falling apart and dangerous.
I discovered that inside, the unit was extremely well built and changing the power cord (and connecting the ground to the transfo frame) was all there was to it. But, the inversion overvoltage can reach easily 30 VAC which is outside of present safety standards and above ratings for digital chips.

As PeFu writes, ideally using a white Märklin transfo is the best option.
Cheers
Jean