Posted 09 July 2009 - 08:48 PM
Different drives will consume different amounts of electricity, called AMPS. If you draw too many amps for a system, it will drag the voltage down a bit.
You didn't say how many amps each 12v supply has. With 650W, it certainly should be enough.
Try unplugging one of the disks that DOES come up and then see if the disks that you say don't come up finally will work. That should rule out whether it is the drives or the power supply.