kernel_task spike when using external monitor

Macbook Pro 2018 with High Sierra

External monitor DELL s2817Q

Connected via DP to USB-C and HDMI, also tried some hdmi hubs.

Randomly the laptop struggle and I see that the process 'kernel_task' goes way up and unless I turn off the display or unplug it it remains like that.

I tried to connect the display on all 4 ports with no change, at some point it happens.

What is more weird is that in some cases (does not work all the times) if I unplug the power also fix the issue. (I also tried to move the power on all 4 ports).

I did a SMC and NVRAM reset already but that didn't work so at this point I bet on faulty USB ports... (all 4??).. if anyone have any advice, i'm all ears.

Thanks.