Fast charge wattage

Apple specifies a 20watt charger for Apple Watch Series 7 Fast Charging.

However, it will charge faster with any charger greater than the previous 12watt chargers.

The Apple Watch Series 7 will ONLY use as much power as it wants, so even if you use a charger greater than 20watts, the Series 7 will only use at most 20watts and ignore the rest of the capabilities of a larger charger.

Yes, because power delivery is a standard for fast charge that can be adopted also by other companies for example Samsung products can also support PD.

But in the link it says that is necessary a third-party power adapter that supports usb power delivery, and in that case you can also use a 5W one.

But if you want to use an Apple one you have to buy one these: Apple 18W, 20W, 29W, 30W, 61W, 87W, or 96W USB-C Power Adapter

And for fast charge you also need the Apple cable that is on the link that I sent before.

You can find all you need to know about Apple Watch Series 7 fast charging on the link below.

About fast charge on Apple Watch Series 7 - Apple Support

Why doesn’t my Apple 7 watch charge a 20 watt charger