Can you reuse your old USB-C phone charger?

Usually yes when both phones use USB-C, but cable rating, USB Power Delivery/PPS support and each phone’s charging limit still matter.

Connector compatibility is only step one

If both phones use USB-C, the cable can usually connect to both. But charging speed depends on the power adapter, the cable's current/power rating and the charging protocols supported by the phone.

“Works” versus “charges at maximum speed”

An older compliant adapter may charge a newer phone safely while failing to reach its maximum advertised speed. Device Fit Check therefore separates basic reuse from peak-performance claims.