[Lexman8]

Your calculations are basically correct so a 9kW supply will easily be enough for charging the T8 (but see below).

It won't be a purely resistive load as there'll be a transformer and/or solid-state converter in the circuit. I'm pretty sure there'll be circuitry in the charger to limit any in-rush current.

As mentioned above, the only issue would be if other appliances were drawing a significant current at the same time, eg a cooker or, specifically, an electric shower.