I used to run my Heavy load 12v devices directly of my car battery charger. I would set it to the 50-amp jump start setting. Just becaues the charger is putting out up to 50 amps, doesnt mean you will over-power your PSU, the PSU will only take how much amperage it needs. If you think about it, a car battery can put out many hundres of amps and cause no harm.
The only problem I ran into using the battery charger, is that the power output is quite a dirty signal, so you may get interference or noise when using it.