An electrical short circuit.
Likely to cause injury, death. If not that - a fire.
Unplug your computer. Do not use.
Use another computer to update your post regarding system hardware specs and OS information.
Provide more information about the computer and displays - how power is being provided.
What all else is involved: electrical outlets, power strips, extension cords, UPS, etc.?
How did you connect those 3 power cables? Are you able to provide a diagram or photos?
If so, do so via imgur (
www.imgur.com).
More information is needed but the immediate priority is to ensure that no one is hurt and that nothing is damaged via a subsequent fire.