Manufacturers differ on USB-C chargers with lower wattage than the original. Apple says a Mac will charge but recommends at least the suggested wattage; Samsung says charging can become much slower or the screen may flicker and advises the original adapter.
Check the PC connection, the setting, cable seating, port lint, temperature and charge level first. If it is still slow, look for PPS in the charger specs: a high-watt charger without PPS may not super-fast-charge.
A 4,800mAh cell is 18.48Wh. Divide by 45W and you get 25 minutes — yet published full-charge measurements run to roughly double that. Here is the gap, calculated output by output.
Qi2 25W is the brand name for Qi v2.2.1, lifting the ceiling from 15W to 25W. But that number only appears when the charger, wall adapter, case and phone all line up.
The wattage printed on a charger is a ceiling. USB PD fixes a maximum for each voltage step, going past 100W requires a separately certified 240W cable, and a 65W three-port charger drops its main port to 35W once every socket is in use.