This paper presents a new cost effective method for a failure prediction of a digitally controlled Switching Mode Power Supply (SMPS). Electrolytic capacitor is known as one of the highest failure rate components in SMPS, so we tried to detect an Equivalent Series Resistance (ESR) degradation of the electrolytic capacitor directly from the data fetched to a digital controller of SMPS. With a SPICE simulation and a Rapid Control Prototyping (RCP) evaluation, we confirm the degradation can be detected by the data at a transient response under a normal operation. Even only 10 percent of a load step change, which commonly occurs in SMPS for servers, causes detectable transient response degradation.