Can I power a monitor directly from my PC’s PSU for a portable build?

The cleaner option is a USB-C portable monitor. Many of them can receive power and video over USB-C, or power over USB-C with HDMI used separately for video. They’re designed for this kind of setup and avoid modifying the PC’s power supply.

It’s technically possible, but an 8-pin PSU connector isn’t a universal monitor power output. Depending on the connector and PSU cable, it may provide 12 V or multiple voltage rails, while monitors commonly require something like 12 V, 19 V, or another specific DC voltage. You’d need the correct DC converter, wiring, fuse protection, and connector for that exact monitor. A direct DIY adapter could damage the display or create a safety hazard.

Older desktop power supplies sometimes had an AC passthrough outlet for powering a CRT monitor, but that was simply mains power routed through the PSU—not power from an internal 8-pin connector. For a modern display, plugging its normal adapter into the same wall outlet or using a purpose-built USB-C or 12 V monitor is much safer and simpler.