I have a cheap tripod that have a 50mm wide arca-style mount.
Is this a standard or some random thing?
From what I can tell all arca mounts' plate are 38mm wide (the distance between the dovetail/rails), but this one is 50mm:
There's actually no such thing as an Arca-Swiss Standard. Different manufacturers that make "arc-swiss" products make them in slightly different width, height, and slant variations. Some work with each other with varying degrees of compatibility, others do not.
In the case of your tripod release plate, however, it is considerably wider than even the most liberal use of arca-swiss compatible and would be considered a manufacturer's proprietary format.
I was wrong assuming brands followed a pattern just because i saw a lot of 38mm dovetail mounts i thought they where some sort of standard.
well, to close this, the 50mm wide dovetail is a style compatible with the following brands:
there are several brands that do generic mounts. e.g. https://www.amazon.com/dp/B019LE53JS?psc=1
btw all the generic ones call out "dji mount" so i guess this is the answer, though i had never heard of dji before. Maybe i'm too out of the stabilizer crowd as this is what their website says they do?