audiazizz :
The issue that i'm having, is it from the psu ? Or from the converter cable? Or perhaps the motherbard?
It's hard to say. Can't diagnose anything with a junk PSU in the mix.
This PSU only has 14A available on the +12V rail, so for all intents and purposes, it's a 168W PSU, not a 380W one. The power-hungry components today utilized +12V power. This was a design made for the PCs of twenty years ago.
Nor would it be a good 168W PSU in 1996. The power supply uses garbage-tier capacitors, brands like Anodia and Yang-Chun, that nobody ought to be using in an applications like this. The manufacturer, Deer/Solytech is a notoriously poor manufacturer.
The first step here is to get the new PSU and send this one for recycling so that nobody ever tries to use this again.