The 6 pin pin adapter is the recommended type. - Right?
Let's suppose that is not the problem.
Here is published data.
Radeon R9 380
Idle = 75 watts
Full = 290 wattsThe X model is almost the same.
So yes, you will need more power to have margin of reliable performance
Still, you would think t the card would at least start up.
But you say the card does not even show anything at all?
Maybe there is some kind of problem.
When you first turn on a motherboard, the BIOS can run on either the built-in or the new graphics card. There might be a setting inside the BIOS setup that has to be set. Look in yu manual for the motherboard.
Does the manual indicate you must disable the built-in video?
This is about fas as I can help.
Maybe somebody else can.