I've found the ability I was referring to, and another as well. Here they are:
ID "IDS_ABILITY_STUNBURST_NAME"
Value "E.M.P."
StringInfo
ID "IDS_ABILITY_STUNBURST_DESCRIPTION"
Value "Unleashes a large shockwave that disables all enemy ships within its radius for a brief time."
StringInfo
ID "IDS_ABILITY_VOLLEYFIRE_NAME"
Value "Onslaught"
StringInfo
ID "IDS_ABILITY_VOLLEYFIRE_DESCRIPTION"
Value "Diverts power from this ship's engine systems to boost the range and rate of fire of its weapons."
StringInfo
ID "IDS_ABILITY_VOLLEYFIREACTIVE_NAME"
Value "Disable Onslaught"
StringInfo
ID "IDS_ABILITY_VOLLEYFIREACTIVE_DESCRIPTION"
Value "Resumes normal movement at the loss of rate of fire increase."
EDIT I've checked the entity files for Sins 1.17, and both abilities are present. They both have an ability and a buff file. The StunBurst ability is an ultimate ability, and the volley is a non capital ability- it doesn't level up.