A controller for controlling a power converter to convert electrical power at an input voltage into electrical power at an output voltage; wherein - the power converter comprises - a first switcher stage comprising a primary winding of a transformer which is arranged in series with a first power switch; wherein the first switcher stage is arranged in parallel to the input voltage at an input of the power converter; - a second switcher stage comprising an auxiliary winding of the transformer which is arranged in series with a second power switch; wherein the second switcher stage is arranged in parallel to a reservoir capacitor; and - a secondary winding of the transformer which is arranged in parallel to the output voltage at an output of the power converter; - the controller is configured to - determine whether the input voltage is greater or smaller than a pre-determined voltage threshold; - operate the first switcher stage to transfer electrical power from the input of the power converter to the output of the power converter, during a first time period when the input voltage is greater than the pre-determined voltage threshold; and - operate the second switcher stage to transfer electrical power from the reservoir capacitor to the output of the power converter, during a second time period when the input voltage is smaller than the pre-determined voltage threshold. - the power converter comprises - a first switcher stage comprising a primary winding of a transformer which is arranged in series with a first power switch; wherein the first switcher stage is arranged in parallel to the input voltage at an input of the power converter; - a second switcher stage comprising an auxiliary winding of the transformer which is arranged in series with a second power switch; wherein the second switcher stage is arranged in parallel to a reservoir capacitor; and - a secondary winding of the transformer which is arranged in parallel to the output voltage at an output of the power converter; - a first switcher stage comprising a primary winding of a transformer which is arranged in series with a first power switch; wherein the first switcher stage is arranged in parallel to the input voltage at an input of the power converter; - a second switcher stage comprising an auxiliary winding of the transformer which is arranged in series with a second power switch; wherein the second switcher stage is arranged in parallel to a reservoir capacitor; and - a secondary winding of the transformer which is arranged in parallel to the output voltage at an output of the power converter; - the controller is configured to - determine whether the input voltage is greater or smaller than a pre-determined voltage threshold; - operate the first switcher stage to transfer electrical power from the input of the power converter to the output of the power converter, during a first time period when the input voltage is greater than the pre-determined voltage threshold; and - operate the second switcher stage to transfer electrical power from the reservoir capacitor to the output of the power converter, during a second time period when the input voltage is smaller than the pre-determined voltage threshold. - determine whether the input voltage is greater or smaller than a pre-determined voltage threshold; - operate the first switcher stage to transfer electrical power from the input of the power converter to the output of the power converter, during a first time period when the input voltage is greater than the pre-determined voltage threshold; and - operate the second switcher stage to transfer electrical power from the reservoir capacitor to the output of the power converter, during a second time period when the input voltage is smaller than the pre-determined voltage threshold.