Direct-current (DC) power converters play an indispensable and crucial role in various systems, particularly in today’s increasing electrification of global energy. The characteristics of DC power converters have garnered widespread attention in the design and practical application of energy-saving systems. General system design not only considers the output voltage and power rating of DC power converters but also factors such features as efficiency, input voltage regulation, output load regulation, dynamic load regulation, and ripple voltage characteristics as specified in the manufacturer’s datasheet. The objective is to provide a stable power supply to ensure the regular operation of the system. However, the characteristics of maximum startup capacitance are often overlooked, and sometimes only numerical values from the datasheet are used as reference, limiting the insight into the startup characteristics curve. The improper assessment of the startup capacitance characteristics may lead to power startup failure or repetitive oscillations, thereby affecting the operational stability of the system. In this study, the in-depth examination of four high-power-density DC power converters is investigated. Firstly, foundational characteristics testing research is conducted. The characteristics of the maximum startup capacitance are examined in this study by constructing and analyzing the experimental environment. In this research, we explain the critical points in constructing the environment for maximum capacitor load testing and compare the differences between passive components for load and electronic load machine simulation experiments. Finally, we complete the experiment in a low-cost detection environment constructed with essential passive components and obtain the maximum capacitor load characteristic curves of the high-power-density DC power converters. This information will become a reference for system design, ensuring the stability assessment of DC power converters under maximum capacitor load conditions. Additionally, sensor integration for real-time performance monitoring further enhances the understanding of startup capacitance dynamics in high-power-density DC power converters.