There are some powered USB hubs that are not compatible with the USB standards.
The XM communications chip should be self powered, but the default from Silabs is powered from the USB. This was causing the comms chip to overheat in our early days if the XM mains power supply was switched off.
Henrik wrote a program to fix this:
All recent XMs should have been fixed, but you can check this using USBview.exe which is in your Spooky2 directory.
An entry for BmAttributes should show a value of C0, not 80. The XM does not have to be powered to read this.
What this means is that the XM has very little power requirement from the USB.
For more details, please check the link: