A Victron MultiPlus is a combined battery charger and inverter: when the system is connected to the grid, it will automatically charge the batteries and provide mains power to all outlets. If the plug is removed from the external grid, the MultiPlus automatically switches to inverter mode: the outlets are powered via the battery and the inverter. The MultiPlus therefore always guarantees 230 Volts!
When power is limited to, for example, 6 Amps at a campsite or marina, this limit can be configured. The MultiPlus or Quattro can provide their inverter capacity in parallel with the grid. This allows you to turn 6A into 16A, for example, so you aren’t affected by the limited current (or blown fuses at the campsite!).