IPA: /ˈʌndəˌpaʊəd/
KK: /ˈʌndərˌpaʊərd/
Having less power than needed for effective performance or operation.
The car felt underpowered when trying to accelerate on the highway.
Underpowered → It is formed from "under-" (meaning below or insufficient) and "powered" (from the root "power" which comes from Old French *poeir*, meaning to be able or have strength). The word describes something that has insufficient power or strength.
Think of something that is 'below' ('under-') the necessary 'strength' ('power') — that's why underpowered means lacking sufficient power.