A transmitter comprises a power amplifier which has an amplifier power-supply input and an output to supply a transmission signal with an output power. A power supply has power supply outputs to supply a first power supply voltage and a second power supply voltage. A switching circuit is arranged between the power supply outputs and the amplifier power-supply input. A controller has an input to receive a power change command to control: first the switching circuit to supply the first power supply voltage to the amplifier power-supply input, and the power supply to vary a level of the second power supply voltage, the level of the second power supply voltage being lower or higher than a level of the first power supply voltage if the power change command indicates that the output power has to decrease or increase, respectively, and secondly the switching circuit to supply the second power supply voltage to the amplifier power-supply input.