No risks (as long as your charger is a good quality one).
Charging slowly is even good for your battery life, as it’s preventing it from heating (sadly setting the charging current is not possible with NOS), and from dendrite formation (bit technical but it reduces the battery life).
The values you can see for power range is due to USB PD or Qualcomm QC protocols (dunno what nothing implements), the charging current and voltage will vary depending on the phone status. (Assuming that the charger and the phone are compatible).
This is controlled by a communication between the phone and the charger, but it does not mean that the phone is restricted to these nominal power values.
Power is Voltage x Current, and current will always fluctuate during the charging…
These values correspond to each levels and are set by : nominal current for the corresponding level x Voltage
BTW, even if your charger doesn’t support PD or QC, your phone can charge with regular 5V just fine, no need to buy a new one 🙂
Only thing to keep in consideration, some bad quality ‘no-name’ chargers (even famous brands sometimes) can output a very nasty signal when power gets too high for them… And you need a minimum of equipment and knowledge to check them.
But if you dont know, stick with independent recommendations 🙂
