>The power supplies are daisy-chained together and they re both plugged
>into the same hub, but other than that there is nothing.

I have seen problems where the external hard disk power supply was not 
capable of supporting extra equipment plugged into it's "daisy chain" 
power connector.  I know, they shouldn't provide a daisy chain connector 
if it loads down the disk supply.  But features are easier to sell than 
quality.

...Harlan