Connecting ATX power supply to motherboard

[Eklmn]

I connect an ATX power supply to a motherboard, it works fine.
Connecting another two ATX power supplies (taken from working computers) to same motherboard does not power the board.

For connection I used only one 20 pin (P1 http://www.support.dell.com/support/edocs/systems/dmag/techovu.htm) connector.

Is it possible that some power supplies need something more to make them work, say jumpers on motherboard?
One of "non-working" power supplies is from Dell Dimension.

Thanks.

 

[Praetor]

Connecting another two ATX power supplies (taken from working computers) to same motherboard does not power the board

A power supply will only deliver power if you turn it on .... now if you dont connect the ATX20/24's then theres no way (short of hacking the PSU) of turning the PSU on. And if the PSU is off then (obviously) it wont power up.

Is it possible that some power supplies need something more to make them work, say jumpers on motherboard?

Yeah ... they need a internal powerup via the ATX20/24s (thats why you have a power button on the computer)

Why are you connecting multiple PSUs to a single machine (which is something you shouldnt be doing)?

Now if you mean that you connected different PSUs to the same mobo independently (as opposed to concurrently), then it wont work because Dell systems are built as to only be able to use Dell PSUs (so you have to buy from Dell etc).

 

[Cromewell]

Yeah, Dell PSUs don't work in anything but a Dell and even then I think they change the P1 connections every couple years

 

[Eklmn]

Sorry for confusion. I connected only one power supply at a time.
Also this is very strange that I can not use Dell power supply with any ATX motherboard (this time it is VIA EPIA MII10000). I thought that interfaces are standard. Usually it is enough to connect P1 and close power pins on mother for a short time. Weird
Thanks for reply.

 

[Cromewell]

the ATX interface is standard, for whatever reason Dell stuff is not