L5 uses USB-C PD3.0 to charger the phone, it is the recommended way. Currently all L5 are not stable on charging, they still have an old firmware, but there is a new firmware to be released which has many improvements in battery charging.
Not all USB-C are PD. and Purism only develops the charge with the original L5 charger, they have not much money to waste it on development, time and testing with old chargers. The old chargers are not safe to charge the L5. You can charge the L5 with any certified usb-c PD charger only for the good performance.
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