You can measure both aspects with a multimeter ohm file:
1, the two outlet resistance should be normal, 220V, 1000W about 48 ohms, 1500W about 32 ohms, and so on.
2, the resistance of any of the outlets and the outer casing is more than a few mega. It is good to be able to pass the above two steps. A multimeter is a relatively sophisticated instrument that, if used improperly, can cause inaccurate measurements and is extremely fragile. However, as long as we master the use of the multimeter and precautions, and be cautious, the multimeter can be durable.