If they are adjustable and the same model, you can "balance" them pretty easily. If you had two 350W supplies (like Ray Wu sells), you could easily connect them both. Put some load onto the Hub and then adjust their voltages to be the same.
If you have a way to measure the amps, that would be best, but volts are easier.
If the voltages won't stabilize, like they are slowly cycling the load back and forth, then abandon the idea. Depending on how they regulate their voltage output, they could oscillate and actually damage each other.
Then again, if they do oscillate when you set the voltages at the same value, then drop one by 0.1 or 0.2 volts so that it lags. That should stabilize them.