if rigs totaly shut down with no error its almost definetely PSU
i had similar problem even with reseter tool ... fan on 1 psu just stopped and it makes overheating of psu and his power-off overheating protection makes its job

and AMD and nVidia cards is realy great description :-D
you can have 2 vegas and 7 80ti and those psu you have are worthless
so please, more specific list of gpus