The HobbyKing version is limited to 5A per channel, whereas the Hitec goes up to 6A per channel (for 2s), but both are "rated" at 50 watts max per channel. The HK one stops incrementing the charge current at 5.0 amps, so for a 2s LiPo it is only using 42 watts (8.4v x 5a = 42watts) The Hitec, when set for 6A, theoretically can use 50.4 watts (8.4v x 6a = 50.4watts).
However, when using more than 2s LiPo, the charger will limit the output to 50watts, so for 3s LiPo (12.6v max), the current would be limited to ~4A (3.96A). For 4s (16.8v max), you'd be limited to ~3A (2.97A).
I love my iMax version (basically the same as the HK one).
As far as a power supply, one that can supply 25A or more is sufficient.