Initially:Short answer: yes.
You don't need a $2000 PSU to power up some LEDs, fans or whatever.
"The device that I'm powering will be planned later "
"Probably a cheap PC or a laptop motherboard of unknown make and model that I got in the mail via 12V to 19V adapter. If for the laptop, the power jack is missing. "
So...the actual answer is a resounding No.