Hello david jacobs2,
Thanks for reaching out to Microsoft Community.
We understand how important the power supply is for your device.
Please check the details below for the power supply requirements of Surface Book 3.
Surface Book 3 13.5" (without Nvidia discrete GPU) = 65 watts
Surface Book 3 13.5" (with Nvidia discrete GPU) = 102 watts
Surface Book 3 15" = 127 watts
Ref: Surface power supplies and charging requirements
Hope this answers your concern.
Kind regards,
StevenK