Look at what charge rate you need. A 6000 mah charged at 1c is 6amps. Two of those at the same time although with two seperate chargers would be a total of 12 amps. You would need a power supply that gives you at least 12 amps. The one you listed at 20 amps would give you enough power for what you described.
Consistency is Redundancy …. Just lots of wheel time.