I use an old Thinkpad laptop with its docking station, and some Intel NUCs as my homelab devices and the multihead systems. The PCBs of the Intel NUCs have a 14V power port that can be used with a small step-up converter from eBay. As the docking station is also @13.9V, the same step-up converter can be used for it, too :)

The monitors were a different story, because it was a bit more complicated. Had to test their PCBs a little before I found out how the power circuit works (so that I don't need ~230V there).