2 power supplie setup on same motherboa

no - just plug it in & boot it up

no you don't

no you don't

Actually, you may need to change a setting or 2 in BIOS setup if you switch from an ATX to an AT power supply.

When you use the ATX supply, you will enable ACPI to allow the ATX supply to turn off on it's own when you shut down the PC.

You need to disable ACPI when you use an AT power supply.

I have also seen a few motherboards where you need to change an on-board jumper when you switch power sources.

It is always best to check the MB manual for complete details.

CAUTION:
Unlessyou are swapping the MB between cases, the power switch for each type of supply are VERY different.
The AT power switch has 120V AC on it!
Make sure the power cord is unplugged before handling any switch wires.

Chas

as D4Dar said, no [but there is a caveat]. AT power supplies are on/off power supplies which means that off is off no [power to the mainboard]. ATX power supplies on the other hand provide power to the mainboard even if the computer is off. This supports sleep mode, hibernate mode and wakeup events [such as wakeup on LAN, Ring, remote wakeup or wake up for scheduled maintenance tasks. As mentioned, AT provides only two modes, On and Off.

Hi
"
ATX power supply is different from AT power supply. It depends a logic circuit on the motherboard to turn it on. Once you flipped the power switch on the ATX power supply to on (some ATX power supplies do not even have such a switch), theATX power supply sends a 5V 720MA current to the motherboard through pin 9 on the power connector. That current is for WOL (Wake-up On Lan) and power on circuits. There is a power-on jumper on the motherboard that connects to the pushbutton located in front of ATX case. When the pushbutton is pressed, it sends a signal to the mothboard, which in turn notifies the ATX power supply to turn on the full power. The location of the power-on jumper on the motherboard is manufacture dependent. You willneed to read your motherboard manual to locate that jumper. At any event, do not try to manually jump-start the power supply without attaching motherboard. Since the power supply is expecting certain sensing circuit feedback to regulate the output voltage, munaully starting it without attaching it to the motherboard could cause damage to the power supply. "

from

http://www.compute-aid.com/atxspec.html

Good luck

Mohamed

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