A phone charger rarely fails all at once — it degrades gradually, and most people keep using one well past when they should.
- Visible fraying or exposed wire near the connector
- Charging only works at certain cable angles
- The charger gets hot even at idle with nothing plugged in
- Charging speed has noticeably dropped compared to when new
Bottom line
Any single sign on this list is worth paying attention to; two or more together is a clear signal to retire the phone charger.