MacBook Pro and Dual Charging

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MacBook Pro and Dual Charging

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We posted this on Reddit but wanted to see what folks here think... We have a series of displays that give our Mac laptops display/network/charging capabilities via the USB C cable. The charging on these displays only push 60 watts. MBPs 2019 16" require 90 from what we've read. Since we only offer the USB C cable to employees at home and at their desks, we've seen folks connect both the USB C cable from the display, and the USB C cable from their 90 watt white brick chargers. Does anyone know if this is a bad thing? Power from 2 sources? Like how is the Mac managing the power when both cables are connected? Any thoughts?

Posted on Aug 3, 2023 10:32 AM

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Grant Bennet-Alder

Level 10

140,291 points

Aug 3, 2023 10:41 AM in response to macfromjacksonheights

Any external power supply that provides "USB Power Delivery" (including certain displays) must negotiate over the USB cable using USB Power Delivery Protocol, and can not 'force itself' on your Mac. The Voltage and Current are delivered only after your Mac requests and the charger agrees to supply power under certain controlled conditions. The computer is in control of the entire process.

Your MacBook Pro uses ‘smart charging’ to charge in the optimum way, and only when necessary. Plugged in is Not necessarily actively charging. There is substantial hardware and software cooperating on battery and charging issues. Simply asserting a charging voltage against one of the interface(s) will NOT successfully charge your MacBook Pro.

It is very difficult to balance power supplied from multiple sources. The literature suggest the Mac intends to choose the 'optimum' source, but practial experience says it tends to stick with the FIRST source connected, in most cases.

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MacBook Pro and Dual Charging

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