It will work (fit). There is no such thing as an ATX 2.0 case. ATX 2.0 (for PSUs) was invented to better serve more power hungry components in your PC.
In ATX 2.0 there must be two 12 V rails. To explain a rail; demands by something on the PSU will only affect devices on the same rail, those on the other 12 V rail, or one of the lower voltage rails will be completely unaffected (unless the PSU catches fire
).
I could buy an ATX 2.0 PSU and switch it for my ATX PSU in my computer right now, no worries.
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