Question

why is water not suitable for extinguishing a fire in a new electrical appliance

Answer 1

Because water is a good conductor of electricity........
If we will throw water, it will conduct electricity that may cause much larger damage

Answer 2

It will extinguish a fire but if the electricity is still running then it is a major risk for electrocution. It also destroys most electronic devices. Once the power is off, water works as well for this as any other fire.