Hi Vaclav,

It is always best to parallel an electrolytic cap with a ceramic. The ceramic will have much lower ESR at high frequencies. I would suggest you try 10 - 100 nF X7R, preferably an SMD for lowest ESL. I would also suggest to add the ceramic to the other regulator, because at the moment it might just be marginally stable.

Good luck.

Regards,
Rob.