Hi jsmith_11,
Welcome to Microsoft Community. It sounds like you're dealing with a common issue when charging devices with higher power demands through USB-C ports that may not be designed to handle them at full capacity. The error message “USB device might need more power” typically means that the connected device is trying to draw more power than the port can provide. While your Surface Book 3’s USB-C port support charging, it might not support high-wattage charging. USB-C ports can vary in their power output, and some may not support the higher power delivery required for newer smartphones.
Surface devices often use USB-C for data transfer, video output, and charging, but the power output can differ depending on the specific port. The lack of clear information on the wattage output for your Surface Book 3's USB-C port makes it hard to know if it’s capable of providing enough power for the iPhone 16.
Charging with insufficient power typically won’t damage your iPhone or Surface. The device will just charge slower. The error is more about the system being unable to provide the full required power at once. Charging devices from USB-C ports that don't meet the required power output is more of an inconvenience than a risk, though it’s always safer to use a dedicated charger.
Your Sincerely Hahn. W - MSFT | Microsoft Community Support Specialist