Due to the increasing use of electronics in critical aircraft control systems, it has become more and more important in the aerospace industry to understand how the degradation process of electronic devices occurs. Power supplies are devices of special interest since their internal components such as diodes, capacitors, MOSFETs (Metal Oxide Semiconductor Field Effect Transistor) and IGBTs (Insulated Gate Bipolar Transistors) operate under continuous stress conditions and often present elevated failure rates. The aim of this work is to present a methodology for detecting the gradual health degradation of a COTS (Commercial off-the-shelf) power supply. An accelerated aging process for power MOSFETs was conducted. During this experiment, power MOSFETs were subjected to thermal overstress in order to increase die-junction temperature above rated value through large current from drain to source. Multivariate regression analysis was applied to the raw data collected during the tests in order to assess the power supply health status.