There’s some discussion around a similar topic that might be useful, though it’s not so specific to your setup. In my experience it’s not so easy for even a higher amperage psu to deliver the promised amount during the heavier draw demands of the startup process.
The reliability and accuracy of the components used in the power supply itself are eventually called into question and even then, those elements are often growingly disproportionate in cost to stability as the price goes up.
Hopefully something discussed here will help point you in the correct direction as my powering needs are probably a bit more simple than yours but I don’t currently have a solution for powering more than a few boxes at a time either. Even a PSU with (in theory) more amps than required, when put into practice, can’t get 4 devices turned on simultaneously without the units all rebooting as each new device was added in.
The PSU with more amps simply can’t keep the flow constant and stable when the new surge from each device’s startup draw occurs.