I found a 5V 4A power supply on ebay that should drive these things up to warp speed on ebay. Not sure how long this link will be valid. If it's dead, just google "5v 4a power supply", or what ever you're looking for.
Don't expect your hubs to power 7 miners on 3 amps of power! 3.5 amps is needed for 7 hubs, perferabaly 4 amps.