To address critical technical bottlenecks in high-impedance fault (HIF) detection—namely, delayed detection and insufficient localization accuracy—in distribution networks, this paper proposes a novel fault-location methodology based on the Differential Power Spectrum Singularity (DPSS). First, a fault-impedance identification technique leveraging low-frequency active-power differences is introduced. Second, a physics–electricity coupled model of HIF is formulated to unveil the mapping mechanism between the power-spectrum characteristics at the fault point and its spatial location, along with an adaptive upper-frequency sweep criterion under dynamic line-scale conditions. Subsequently, an offline validation platform for a 10 kV single-phase cable is developed by integrating PSCAD-based electromagnetic transient simulations with Matlab signal-processing algorithms to systematically evaluate the robustness of the DPSS indicator under diverse operating scenarios. Experimental results demonstrate that the proposed method consistently suppresses HIF localization error within 0.2% under complex operating conditions, substantially outperforming existing techniques and thus validating its effectiveness and reliability from both theoretical and practical perspectives.