The Raspberry Pi 4 was announced two weeks ago as a major new upgrade to the line of cheap single-board hobbyist computers. The Pi 4 featured a faster CPU, options for up to 4GB of RAM, and a new, modern USB-C port for power delivery. The Pi 4 was the Raspberry Pi Foundation's first ever USB-C device, and, well, they screwed it up.
As detailed by Tyler Ward, the Raspberry Pi 4 has a non-compliant USB-C charging port and doesn't work with as many chargers as it should. Thanks to the open nature of Raspberry Pi (even the schematics are online!), Ward was able to discover that Raspberry Pi just didn't design its USB-C port correctly. Two "CC" pins on a USB-C port are supposed to each get their own 5.1K ohms resistor, but Raspberry Pi came up with its own circuit design that allows them to share a single resistor. This is not a compliant design and breaks compatibility with some of the more powerful USB-C chargers out there.
Whether your USB-C charger works with the Pi 4 has to do with whether it uses an "e-marked" cable. E-marked cables are fully featured USB-C cables with chips inside that negotiate power management, accessory modes, data rates, and other communication specs. Since the Pi 4 USB-C port is wired incorrectly, these smart cables will detect the Pi 4 as an "Audio Adaptor Accessory" and refuse to charge them. Usually, e-marked cables are more expensive and come with larger, higher-powered items, like a USB-C laptop.

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