Computer-implemented systems and methods for modeling low-dropout (LDO) regulators and charge pumps are provided. A relationship between an output voltage of an LDO regulator or charge pump and a loading condition is determined. A frequency-domain analysis is performed at multiple frequencies to determine an impedance function representative of an impedance of the LDO regulator or charge pump at each of the multiple frequencies. A vector-fitting algorithm is applied to approximate the impedance function using a plurality of poles and residues. A circuit is synthesized based on the plurality of poles and residues. A model for the LDO regulator or charge pump is generated, where the model includes the synthesized circuit and components that model the relationship between the output voltage and the loading condition.