ESP8266 resets during Wi-Fi activity: how should the power supply be tested?

Capture the voltage close to the module during the failing operation with a suitable oscilloscope probe connection. Short transients can be invisible on a multimeter. Compare the minimum observed voltage with the module's operating requirements and inspect reset or boot messages for supporting evidence.

Check regulator transient response, input headroom, connector resistance and return paths. For a simplified capacitor-only estimate, ΔV = I × Δt / C, but this ignores ESR, trace inductance and the regulator's response. Adding a large capacitor blindly can conceal the actual weakness without making the supply reliable.

Run a repeatable network workload and change one factor at a time: a known adequate supply, shorter leads or corrected local decoupling. If the rail remains within specification, examine watchdogs, stack use and invalid memory accesses. Keep power measurements and firmware logs aligned in time.