Thanks for your answer @dh04000 !
But Recalbox seems to recognize it as a "Twin USB Joystick". If I plug the two blue adapters I have, RecalBox recognizes 4 controllers... If I map the buttons on the controller plugged in the 2nd USB port, Recalbox configures the 3rd controller. So that all seems logical. The issue seems somewhere else.

Hi to all,

I just bought two blue triangular twin PS1/2 to USB adapters from Ebay. Both are working correctly with the PS1 controller but I'm unable to use my PS2 Dualshock. I tested the PS2 controller with a PS1 console, it's working. When I try to map the PS2 controller in Recalbox, I can only switch the analog switch but I cannot map the buttons since pressing them does nothing.
What am I missing here ?

Thanks !!!
Piotr.