Great recap of your situation! You'd be surprised how often that kind of info needs to be dragged out of people over a series of fifteen posts.
To summarize a response to your latest:
1) You should have all the power you need with that PSU, no matter what rail kerjiggery they are using.
2) Does the drive have a hardwired USB cable or is it removable? Is it a USB 3.0 drive? If so, are you using a USB 3.0 cable?
3) Do you have another computer you could try the questionable card in? If it won't work there either, you may just have a dud USB card.
4) Does any other USB device work on the iffy card?