Not quite. It's the product of voltage x amperage that determines wattage. If you have more volts you need fewer amps.

A charger's wattage is simply a rating of its maximum output, but this determined entirely by the power supply Assuming you have a charger that can handle 24v input, it doesn't matter whether the power supply puts out 12v @ 40 amps or 24v @ 20 amps, the power output is 480 watts. But if you use an Iota PS @ 45 amps x 13.8v and a Meanwell @ 43 amps x 24v, the charge time is a LOT faster with the Meanwell.