Demolition Expert

Demolition Expert is a perk in Fallout 2, Fallout 3, Fallout: New Vegas, Fallout 4, Fallout 76, Fallout 2d20 and Fallout Tactics. It is also a skill that was to appear in the canceled Fallout: Brotherhood of Steel 2 (skills in this game work like perks do in other Fallout games).

Fallout 2 and Fallout Tactics
For characters that like to blow things up, there is nothing better than this perk. Explosives set by this character do more damage and always detonate on time.

In Fallout 2, dynamite and plastic explosives cause an additional 10 points of damage.

Fallout 3
With each rank of this perk, your character will do 20% more damage with mines and grenades.

Affected weapons
Although weapons such as the missile launcher and Fat Man fire explosive projectiles, they are considered Big Guns and are not affected by this perk. However, the Fallout 3 Official Game Guide claims that the perk does work on missile launchers.

Bugs

 * The Nuka-grenade is not affected by this perk.
 * Grenades and mines used within the Anchorage Reclamation simulation are not affected by this perk.

Fallout: New Vegas
With each rank of this perk, your character will do 20% more damage with all weapons governed by the Explosives skill.

Note that this damage bonus only affects the actual explosive part of the weapon's damage, not the physical impact. For grenades and mines this is a negligible difference as they typically only deal 5 physical throwing damage at most. But for a Fat Man (GRA) it is much more significant as 400 of its 1000 base damage is from the physical impact.

Affected weapons
Prior to patch 1.4.0.5xx, the Demolitions Expert perk only applied to weapons listed in a specific Form List, which contained a few notable (and undesired) omissions. The patch subsequently expanded the Demolitions Expert perk to apply to all weapons governed by the Explosives skill, unique, DLC, or otherwise. For reference, a full listing of Explosives-skill weapons follows.

Fallout: New Vegas Explosives skill weapons, 2

Fallout 4
Demolition Expert increases the damage dealt by thrown grenades, mines, explosive weapons such as the missile launcher and Fat Man (these also stack with the Heavy Gunner Perk) and even the legendary Explosive prefix.

However, it does not increase the secondary damage dealt by said weapons (e.g. a grenade that deals 2 types of damage). In this case, it will only increase the damage of the first type. That also means that this perk does not increase the damage of pulse mines and pulse grenades because they only deal secondary energy damage.

Bugs
Should this fail - Use the console command 'player.removeperk' for all levels 1-4 and either re-select/enable these perks through normal Tab-T entry or 'player.addperk' commands.

Fallout 2d20
When making an attack using a weapon with the Blast quality, the attack gains the Vicious damage effect.

In addition, unlock explosives recipes which have this perk as a requirement.

Fallout: Brotherhood of Steel 2
Increased Critical Chance to all explosive weapons.