I purchased the 5V 1A USB port power supply, http://adafruit.com/products/501, and while it works fine, it emits a high frequency whine. It is not really loud, but noisy enough that sitting next to it is annoying.
I found this post,
but this seems different, I would call it more of a whine than a hum and a high enough frequency to be unpleasant to be around. I have plenty of "wall warts" around the house, and this is the only one that makes enough noise for me to notice.
Is this expected, or does this power supply have some defect? I was going to just buy a second one as they are cheap, but don't want to if the next one is likely to have the same issue.