Which music plays in episode 126 on Android 17 vs Toopo?
After a bit more search I found it. Its the "Theme of Gohan" by Norihito Sumitomo.
Can't find the original OST but there is a recreation which is quite close to it by a guy named "PokeMixr92"on Youtube.
Here is the link : https://www.youtube.com/watch?v=guuVnTQavSc