[connicpu]

Power regulators that can efficiently produce the 1-1.5v output with the most minimal noise generally have lower maximums on their input voltage as well. In designing some of my own IoT devices I've looked into a fair number of power regulator ICs and 36V is a common maximum input voltage. The efficiency curves on the datasheets also usually show the efficiency gets lower the higher the input DC voltage. In a power regulator, inefficiency means even more heat you have to dissipate, not great in a GPU. I'm sure the GPU would love to take even lower voltage if it could, but 12V is the compromise we've decided on to get decent efficiency without requiring insanely thick conductors.