Controller and method for a power converter. For example, a controller for a power converter includes: a feedback detector configured to receive a feedback voltage, sample the feedback voltage, and generate a sampled voltage based at least in part on the feedback voltage, the sampled voltage being associated with one or more fluctuations in magnitude; a resistor selector configured to receive the sampled voltage and generate one or more control signals based at least in part on the one or more fluctuations associated with the sampled voltage; a variable resistor network configured to receive the one or more control signals, determine a network resistance based at least in part on the one or more control signals, and output a compensation voltage based at least in part on the network resistance; and a voltage generator connected to the variable resistor network and configured to receive the compensation voltage.