Startech PEXUSB3S23 PCI card

Is there any reason to believe that this 2 port USB3.0 card shouldn't work in a Dell Optiplex 990?  Both myself and a coworker have installed this card in the open PCI slot in our systems and neither works properly.

If you install the card out of the box, it enumerates and you can install the drivers from the disk.  If you plug anything into the port, it is not recognized.  I first tried my Western Digital Passport external hard drive, and the lights never came on.  Startech mentions that you can use the optional SATA power connector to provide the full USB 0.9A spec, so after locating a suitable SATA power extender (there a no extras on the power supply), I found that the card works better, though not reliably.  It still won't run my external hard drive (now it lights up, but never shows up as a device) nor a piece of small lab equipment, both of which run properly on every other USB 3.0 port to which I've ever connect them.  It will apparently run my Cypress USB 3.0 development kit.

It feels like a power problem, but googling the Startech card doesn't seem to indicate that anyone is having any of these issues in other systems, especially after connecting external power.