I did not factor in headroom for peripherals or fast charging. Personally I don't have use for either.
What I would like to see covered are all GPU's that require a 6 + 8 pin auxiliary PCI-e power connection. I'm by no means an expert on this but from what I can gather a 6 pin connectors will supply +75W and 8 pin +150W, so a total of +225W external power to the GPU in addition to 75W coming from the PCI-e slot - a total of 300W power dedicated to the GPU. In order for 300W to be directed to the GPU, a 375W PSU would, to my understanding, be a pretty good match as PSU's are only about 80% efficient.
Note: The PCI-e slot could either be supplied by the PSU (as I assumed above) or draws from the host device via Thunderbolt. Thunderbolt 3 is ratet for 100W as far as I know. A 300W PSU + 75W via Thunderbolt might therefore also work... (?)