Let's say I have a ranger who is using the optional feature "Favored Foe" from TCoE (p. 56):

When you hit a creature with an attack roll, you can call on your mystical bond with nature to mark the target as your favored enemy for 1 minute or until you lose your concentration (as if you were concentrating on a spell).

The first time on each of your turns that you hit the favored enemy and deal damage to it, including when you mark it, you can increase that damage by 1d4. [...]

Also, here's the text for hunter's mark, PHB p. 251:

You choose a creature you can see within range and mystically mark it as your quarry. Until the spell ends, you deal an extra 1d6 damage to the target whenever you hit it with a weapon attack [...]

If my ranger was already concentrating on hunter's mark, and hits the creature currently "marked" by hunter's mark with a weapon attack, if I were to then use Favored Foe, would the damage from both be applied?

Obviously concentration on hunter's mark would drop because I'd now be concentrating on Favored Foe, but since this is applied "when you hit" and the damage from hunter's mark is also applied "whenever you hit", would the damage from both features be applied to that attack?

This would be useful if you score a critical hit and don't mind "losing the spell" for some extra damage, for example.

So which outcome would be considered the RAW way of resolving this:

1. As the Favored Foe feature is applied "when you hit", as is the hunter's mark damage, both happen simultaneously, so the damage from hunter's mark has already happened by the time the spell drops. Therefore, the damage would be "standard weapon damage + hunter's mark damage + Favored Foe damage".

2. Because Favored Foe would result in concentration being dropped on hunter's mark, only one or the other can be true at the time where damage is resolved, so assuming the ranger did use Favored Foe, the damage would be "standard weapon damage + Favored Foe damage".

Let's say I have a ranger who is using the optional feature "Favored Foe" from TCoE (p. 56):

When you hit a creature with an attack roll, you can call on your mystical bond with nature to mark the target as your favored enemy for 1 minute or until you lose your concentration (as if you were concentrating on a spell).

The first time on each of your turns that you hit the favored enemy and deal damage to it, including when you mark it, you can increase that damage by 1d4. [...]

Also, here's the text for hunter's mark, PHB p. 251:

You choose a creature you can see within range and mystically mark it as your quarry. Until the spell ends, you deal an extra 1d6 damage to the target whenever you hit it with a weapon attack [...]

If my ranger was already concentrating on hunter's mark, and hits the creature currently "marked" by hunter's mark with a weapon attack, if I were to then use Favored Foe, would the damage from both be applied?

Obviously concentration on hunter's mark would drop because I'd now be concentrating on Favored Foe, but since this is applied "when you hit" and the damage from hunter's mark is also applied "whenever you hit", would the damage from both features be applied to that attack?

This would be useful if you score a critical hit and don't mind "losing the spell" for some extra damage, for example.

So which outcome would be considered the RAW way of resolving this:

1. As the Favored Foe feature is applied "when you hit", as is the hunter's mark damage, both happen simultaneously, so the damage from hunter's mark has already happened by the time the spell drops. Therefore, the damage would be "standard weapon damage + hunter's mark damage + Favored Foe damage".

2. Because Favored Foe would result in concentration being dropped on hunter's mark, only one or the other can be true at the time where damage is resolved, so assuming the ranger did use Favored Foe, the damage would be "standard weapon damage + Favored Foe damage".