bonjour cher Monsieur
The current is easy to measure with a sensitive AC ammeter, low range DVM. as the main voltage is fair stable, just multiply by 240, 120 for watts.
We use Fluke or similar DVM, lowest AC current or Keysight 34465a.
Alternative make a current senses series shunt, 1,10, 100 ohms.
Just measure the voltage drop.
Keep load off so the meter sees only the standby current.
Easier to just get the spec of the device
Bon chance
Amicalement
Jon