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

Im with this guy. we need to know if you on the type of gpus you have. and also are using 110v or 220/240v outlets also. PSUs will say its for a certian wattage amount, but it has to be on the right voltage to give that much juice also.