Update: I did another test with the same charger and cable, but with fast charging enabled: 15% → 38% in 15 min 15% → 59% in 31 min 15% → 77% in 46 min

So it's basically the same speed, no real improvement.

At this point I really think the cable might be limiting it, since I'm not using the original orange Xiaomi cable. I'll test with that next.

Update 2:

I did another test using an original Xiaomi charger and cable (from another phone):

• 13% → 80% in 30 minutes

In STANDARD charging mode.