Hold on, now:

Every USB port outputs the same voltage and current; otherwise, our devices wouldn't work with every single USB port. Therefore, any component that the USB cable plugs into should either work with every USB device or with no USB device.

The only way that these devices could differ from each other is in their tolerance -- that is, maybe my phone can tolerate a higher charging voltage, higher current, higher ripple (that is the divergence from DC), etc. than my iPod. However, a standard USB port's output must be sufficient for both of these devices.

I just noticed on the adapter that it's stated that the output is 5.17 V DC and 0.7 A. From a quick internetz search, it appears powered USB ports output 4.75-5.25 V and a maximum of 0.5 A current. I guess I need to see if my iPod can tolerate 0.7 A at 5.17 V, but that doesn't tell me if other aspects of the adapter (particularly the ripple) are tolerable by my iPod.

Quote Originally Posted by Atmosfear View Post
I'm not saying it won't work, but USB power isn't as universal as you think.

I've got USB power cables that simply won't power my blackberry. Likewise, my blackberry cable will not power my external hard drive. I don't know enough about batteries to tell you what the risks are in terms of cell memory, overcharging, and burnout, but I would err on the side of caution.

I've got 2 different blackberry models, and use the same USB and wall chargers on each with no problem, but I wouldn't trust it to another device.
My case is a little different. I'm actually using the cable that came with the phone as well as the cable that came with the iPod. However, on the male USB end of the iPod cable, I want to use an AC adapter that was originally intended for the phone.

As for your Blackberry's cable not working with your external HD, it's possible there are also electrical components in your cables that render them incompatible with other devices, but that seems unlikely...