As the price of ATX PSU's has skyrocked, i would suggest using server psu with breakoutboard:

Buy a complete kit or build your own.

https://www.parallelminer.com/product/build-your-delta-platinum-94-1400watt-200-240v-power-supply-kit-for-gpus-mining-zec-dash-eth/

or find a pus 40-60$ on ebay + breakout board 15-30 $