This should help:

https://www.reddit.com/r/raspberry_pi/comments/2wgty6/how_do_i_connect_a_ps2_controller_directly_to_the/

@jamaisviciara do not post the same question on multiple old threads. You should start a new topic - Please do not post a support request without first reading and following the advice in https://retropie.org.uk/forum/topic/3/read-this-first

@agour Have you ruled out the adapter at all? Does it work fine on a PC? Also, are you using a Libretro based emulator, as the retroarch configs only apply to them.

@dankcushions Was rather lookin' for some "solved" button? Really, this forum engine is far too confusing for old people. "Terminated" problem? You know what I mean? Does it even makes sense, hahaha? I liked the old forums' engines.

Thanks!