The Samsung EPAP‑420 is a 420 W AC‑to‑DC power supply designed for industrial control systems, accepting 100–240 VAC at 47–63 Hz and delivering up to 8 A output. Common failure modes in this class include capacitor degradation (especially electrolytic), fuse blowouts, and overheating of the internal switching regulator; symptoms often manifest as no output voltage, excessive heat, or audible noise from the transformer. First‑check diagnostics: verify input AC voltage and polarity with a multimeter, inspect the main power fuse and any inline fuses for continuity, then measure the DC output rails (±12 V, ±24 V) while monitoring temperature of the regulator IC and capacitors for abnormal rise.[oss-gpt-20b]