Need internal power cable for early 2008 mac pro

To add some additional information for the curious:

Highpoint makes two cards, marketed for the Mac Pro. Both seem similar to cards they market for PC's, and the cards may in fact be identical hardware - I don't know. The Highpoint Mac cards do cost more than their PC counterparts. But, they come with Mac drivers.

I purchased the higher priced card, a 4 port USB 3.0 card, the 1144AM, which also has RAID support (which I didn't need). With the Mac drivers installed, this card sort of worked on my Mac Pro (early 2008 - 3,1) I could connect a USB 3.0 external disk (a 3 TB WD drive mounted in a Rosewill USB 3.0 enclosure), and the drive worked at USB 3.0 speeds; I was able to write zero's to the entire 3 TB drive in about 6 hours). However, there were several "gotchas". The card only worked with hard drives, not with several USB 2.0 devices, such as memory cards, that I tried. The card is supposed to be fully backwards compatible with USB 2.0 devices.

Also, and more importantly, I have an Apple branded ATI 5770 card in my Mac, which has a known "bug" - the computer occasionally wakes from sleep with a fuzzy screen, requiring that I sleep and rewake the computer. This bug occurs once or two twice a week, but it occured much more often with the Highpoint card installed. So often, that I removed and returned the highpoint card. My impression, and its only an impression, is that the highpoint card was drawing a bit too much power, at least for my 5770-equiped Mac, and that power fluctations of the bus voltage were interfering with my ATI card.

My Mac Pro also boots windows 7, and with the highpoint windows 7 drivers installed, the card worked as well, but I would sometimes get Windows error messages that there was a voltage or power issue with the card, and that the USB 3.0 ports were being shut down. I had to reboot to correct this.

Now, the highpoint 1144AM card I was using plugs in to the Mac Pro's PCIe slot and does not accept an secondary power source.

Highpoint also makes a 2-port USB 3.0 card, the model 1022AM. It too is similar in appearance to a the highpoint PC 2 port PCIe card. Unlike the 4-port card I describe above, the 2-point card has a 4 pin molex connector for a secondary power cable. Most PC's have these coming from the power supply. That is what I wish to use, to hopefully overcome the presumed power issues I was having the the 4-port highpoint card.

I do not fully understand why the 2-port card takes an external cable and the 4 port card does not. USB devices, as I understand it, can be either bus-powered (they get their power from the USB cable) or externally powered - they have their own power supply (usually from an AC adapter). It may be that the 2-port card supports bus-powered devices, whereas the 4 part card, lacking a secondary power connection on the card, does not. I don't know.

I want to try the 2 port card, but I need a cable to do so, to hook up the card to my Mac. As best I can tell the way to do this is with a cable that converts the 6 pin power connector on my motherboard to a 4 pin "PATA" type plug.

(to be complete, I do have such a power connection on my Mac Pro, in the optical drive bay. But both optical bays of my Mac are occupied, and for a couple of reasons I don't think I can use a Y-cable)

And, as a final note, the Mac OS does not natively support USB 3.0, you need a USB 3.0 card that comes with driver software. Aside to Apple: the mac pro is supposed to be expandable, you really should provide an OS-native driver.

No, I didn't. I presently don't have a USB3 port on my Mac. I plan to revisit the issue, now that Mountain Lion is out, which does offer some degree of USB3 support (since USB3 is included on newer Macbooks and I think iMacs)