Yes! Thanks! That was my issue! I totally forgot I had no more common ground between the two as I was using distinct power adapters. Adding a cable that connect to the ground pin on the motherboard, alongside the 5v cable for EN, solve the issue.
(Also note for other users, but I was still powering my powering my motherboard with a 12V power adapter. Powered this way, it didn’t yield any result. Only when I powered my motherboard with his original 19V power adapter that the pull-down worked, with the converter outputting 12V)
Thanks a lot for your help!
Ya I know it’s not the right colour norm. 
It was the first thin cable that came under my hand. I should not tell you that I used a red cable for the common ground. 