Capacitive Touch Faucet Solenoid Battery Box vs AC/DC adapter
There are a few issues that might cause the relay &quot;chattering&quot;:

If the &quot;wall wart&quot; (power supply) is poorly isolated from the mains, AC could be getting into the sensing circuit.

Remedy: try a different type of power supply.


If the power supply is high-efficiency, e.g., using high-frequency PWM to control output voltage, some radio-frequency interference may be causing the issue.

Remedy: try a different type of power supply.


The power supply might not provide enough current for the demands of the solenoid.

Remedy: Put a large electrolytic capacitor or a supercapacitor across the supply. Mind the polarity and voltage requirements, particularly for the supercapacitor. Or try another suply, with higher current rating.



N.B. To reduce the danger of electric shock and of fire because of current flow to ground, use a grounded power supply.