ATX-Naomi power supply question

[WigglesWorth]

So after doing some searching and people suggested to get a ATX power supply and get a Naomi to Atx cable. Alright that is a cheap option i shall do...now heres the thing that confuses me.... The capcom i/o converts 5 volts to 3.3 i get that but how would one get the PC power supply provide exactly 3.3 volts and 5 volts properly. Again new at this so im unsure if im asking the right question

[nem]

An ATX PSU has multiple rails, see here for all the outputs:

https://en.wikipedia.org/wiki/ATX#Power_supply

All of the main voltages are auto-sensing, so there's no need to dial in voltages. ATX spec dictates that these voltages must be within +-5%, which for 5V means a range of 4.75V to 5.25V.

Personally I much prefer the original SUN PSU for a Naomi and I would never use anything else.