I have a battery charger that I haven't used in years. When I plug it in I know it has powerbecause I hear a hum. Without having a battery is there an easy way of telling whether it is putting out a charge.
Attatch it to a 12V light bulb or bulbs. A standard trailer light bulb would be around 5 watts which would be a little less than 0.5A. It won't tell you that it can put out full current output but at least tell you it is alive.