The circuit (10) has voltage terminals (18,32), and a power converter circuitry (42) that is provided with a switchable element and an inductor (44a). The power converter circuitry is provided between the voltage terminal (18) and the voltage terminal (32), and performs voltage switching between the direct voltage (V18ab) that rests against the voltage terminal (18) and the direct voltage (V32ab) that rests against the voltage terminal (32). A controller (12) controls the power converter circuitry with a variable switching frequency. An independent claim is included for a method for adjusting power of circuit.