All PSUs drop voltage a little under load. The core ATX specification allows a a +12V tolerance of ±10% (10.8V-13.2V), but most PSU manufacturers adhere to the ATX2.x "recommendations" for a +12V tolerance of ±5% or less (11.4V-12.6V). PSUs which meet 80 Plus standards (Bronze/Gold/Silver/Platinum/Titanium) typically require better design/components which intrinsically offer tighter voltage regulation.
To be honest, any PSU these days which lacks Active PFC and can't offer (at worst) ±1% regulation is best avoided. It will be inefficient, hot, loud, and have to work harder to deliver the same power load, and the "dirty" power it outputs will be a lot more wear and tear on the (already hard-working) motherboard-integrated VRM circuitry.
I think a 750W PSU would be the minimum recommended for your listed hardware.
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