Can I use a second power supply for hard drives?

I have an old Pentium-M based Shuttle PC that is great as a backup NAS solution at home, where I prefer low power consumption over speed.

It only has two SATA ports. However it has a PCI slot and I have a 4-port PCI card.

So my plan is this:

• Put the Pentium-M, PCI card, etc. into a case and let it use its native power supply (which is an external brick)


• Install a second 450W power supply in the case and use it to power 4 SATA disks. Their SATA connectors would then plug into the PCI SATA card.

To be clear...the second 450W would not be plugged into the Pentium-M's motherboard Only the HDD power (and maybe some fans).

However...would the second 450W power supply actually spin up? If I power it on, would it supply power to the hard drives, or does it need to be plugged into a motherboard to actually provide juice?