What's the purpose of both of these usb plugs on the cable?

almost looks like to me on is male one is female so you can use the usb plug for more then one piece of hardware thats my guess

Guessing is bad.

On another note. the dual usb is needed to supply power to the drive. USB is limited on power it supplies. Thus, they add a second usb. Like 2 power plugs

Plug them both in if it doens't power up.

I got one myself. You HAVE TO plug in both USB to work. The one with the pass-thru is only used for power. If you want, you can just plug the other one into the end of that one. I've seen other (cheaper) models that don't have the pass-thru dongle, and that's a pain.

Yeah I figured that's what it was for and how i've always used mine. The WD Passport externals just have one usb plug .. I use my passport to travel with in my laptop case cuz it has a short cable with only one usb.

That's actually the first time I've seen/heard of two USB plugs to be used like that for power. I just always assumed they came with an AC power source like mine did.

That's the reason I got the Nexstar drive, cuz ya don't need an AC plug.

seriously cool!

i have a nexstar of that type. i have a 100GB 5400rpm drive in it and i only ever needed the nonpass-through USB plug for it to work right. also, my nexstar has the option for an external power source to be plugged in if you plan on using a drive that requires more power.
now, i broke my stock nexstar USB cable a few months ago and have been using a 10ft USB-A to mini-B cable with zero issues.

Excellent I have one of those kind of cables from a junked mp3 player .. trying it now .. if it works it'll be perfect.

I've done a lot of reading on this cable issue today and I have seen 3 different ideas on what the 2 usbs are for.

1: Another plug needed for more power.
2: The pass-thru is only needed when something else needs to plug into the usb at same time.
3: The pass-thru is only needed on USB 1.1 systems for more power.

Then this straight from Vantec ...

did it end up working?

Well there ya go, might as well get the more expensive option!

Yes the usb cable from my camera (thought it was from an mp3 player originally) works fine with this drive .. it's a 40gb WD. I transferred about 14 gigs of data to and from the drive and no issues.