How to power Raspberry Pi 4B 8GB RAM from desktop without undervoltage issue?
You can power Raspberry Pi using your desktop 12VDC output from Power Supply Unit. But, make sure to have a 5VDC buck converter because you need to stepdown 12VDC to 5VDC before being fed to the Raspberry Pi USB-C power input.
Be careful and do at your own risk though. A small mistake and you could fry your hardware.