What power adapter is required for the Apple Watch Magnetic Charging Dock

Rudegar is correct. If you want to take advantage of the Series 7 Fast Charging ability, you'll want to buy a 20w USB C charging plug. Apple, Best Buy and Amazon all sell one. I particularly like the Anker Nano 20w USB C plug, which Best Buy sells for about $16.

does not matter, as long as the connector fits, it's 5volts and minimum 5watt

I'll second the lobster's recommendation on the Anker Nano.