An RF supply system in which a bias RF generator operates at a first frequency to provide a bias RF output signal and a source RF generator operates at a second frequency to provide a source RF output signal. The RF output power signals are applied to a load, such as a plasma chamber. The source RF generator detects a triggering event. In response to the triggering event, the source RF generator initiates adding frequency offsets to the source RF output signal in order to respond to impedance fluctuations in the plasma chamber that occur with respect to the triggering event. The triggering event detected by the source RF generator can be received from the bias RF generator in the form of a control signal that varies in accordance with the bias RF output signal.