The Eldritch Knight fighter's Arcane Charge feature says:
At 15th level, you gain the ability to teleport up to 30 feet to an unoccupied space you can see when you use your Action Surge. (PHB, p. 75)
Is a Fighter really able to use Action Surge, and thus Arcane Charge, even while surprised simply because it does not use up any sort of action/bonus action/reaction?
Best Answer
No, action surge can't be used while surprised in this context
Arcane Charge says:
To use an ability, you must do (and thus be able to do) whatever that ability is allowing you to do.
Action Surge says:
So, using Action Surge requires you to take an action. If you aren't doing that you aren't using the ability at all. You can't just call out the name of an ability, not do anything that the ability says, and then claimed you have used it.
In 5e, there no such thing as an action declaration phase. You don't declare doing something before doing it. So doing it simply means doing the thing that the ability describes. Saying "I use Action Surge" is the same thing as saying "I do the thing that Action Surge says I do".
The Arcane Charge itself seems to support this interpretation:
Note how it does not list not taking the action at all as an option. This supports the argument that "using" Action Surge means using that additional action.
Since being surprised prevents you from taking any actions, you cannot take the action from Action Surge. Since you cannot use the action from Action Surge, you cannot use that ability. And since you cannot use the ability, you cannot benefit from Arcane Charge.