Currently, the 120W charging power of the China-only Mi 10 Ultra is the fastest available, as the battery has to have the respective chemistry, and the phone the suitable charging circuitry for that ultrafast charging session, too.
There are more widespread runner-ups, however, like the Oppo Find X2 Pro or the new OnePlus 8T that come with 65W charging that tops up a 4500mAh unit in less than 40 minutes from depleted state.
Make of it what you will but either the fast 65W charging will be a prerogative for the more expensive S21 models like the Ultra, or you will have to buy the 65W brick separately, like the 45W one that Samsung sells now. Both cases will be fine, however, provided that Samsung gives us the wherewithal and the charging circuitry to pump the Galaxy S21 models with 65W power.
