The better chargers are DC only. Better charger usually means higher amperage, and can maintain that amperage longer through the charge. You also get better features out of higher end chargers like cycle charging, discharging (and at higher amperage), internal resistance checks, etc.

I would not get a PS less then 20 amps, and would go higher if you can afford it. I have never used the computer power supply conversions, but they are inexpensive options as well for good amperage.