Objective: This study characterizes the effects of external conductivity on electroporation to develop methods to overcome potential patient-to-patient variability. Impact Statement: We demonstrate that constant power pulsed electric fields (PEFs) achieve consistent treatment outcomes despite variations in conductivity, thereby improving the predictability and efficacy of electroporation-based therapies. Introduction: Electropermeabilization-based therapies typically deliver static voltages between electrodes to induce cell permeabilization. However, tissue conductivity variations introduce uncertainty in treatment outcomes, as the tissue-specific electric field thresholds that induce electroporation also depend on the extracellular conductivity. Methods: Cell-laden hydrogels were fabricated with varying extracellular conductivities and treated with constant voltage PEFs. The voltages and currents were recorded to calculate the applied powers, and the reversible and irreversible electroporation thresholds were quantified using cell-impermeant and viability assays. Homogeneous and heterogeneous multi-tissue finite element models were employed to simulate the impact of tumor conductivity variability on the outcomes of reversible and irreversible electroporation for constant applied voltage, current, and power PEFs. Additionally, an in vivo murine pancreatic tumor model assessed the correlation between PEF delivery and treatment efficacy. Results: The In vitro experiments revealed that the electric field and current density thresholds were conductivity dependent, whereas the power density thresholds remained stable under variable conductivities. Computational modeling indicated that constant power PEFs best predicted tumor coverage in both homogeneous and heterogeneous multi-tissue models. Similarly, the in vivo tumor responses were also better predicted by applied power rather than voltage or current alone. Conclusions: Applying constant power PEFs enables consistent electroporation outcomes despite variations in conductivity.