what adapter can I use to connect the power and a usb webcam to my only usbc port on macbook retina 12 2017? is this compatible with macbook 12 retina https://support.apple.com/kb/sp757?locale=it_IT ?
You need to look for a USB-C PD dock or hub. Make sure it doesn't use more than 30W, including what it needs for itself, as this is the most the Macbook's charger can provide.