I'll give that a go -
I have 3 x 10 usb hubs , which are rated to 5 amps each and have 5 amps going into it plugged into the wall and into usb port - they are running 9 in the hub + a usb fan to keep them cool.
That's still kinda pushing it, even though you are getting 5 amps at the source, running 9 USB Erupters on that is over working your power supply. Try (if you can) to not use more than 7 per each hub with that power supply.