It is not wise to choose a PSU rated to the maximum load of the charger, I would say the 250w is recomended.

But power is not about the PSU but the load that the charger will make. If you charge 500mA mini drone batteries you can use a 20 watt power supply. But if you connect a 1000 watt supply the charger will not be blown up, the charger will only take what it needs.