#### Answer

$S=\{a,f,m,c\}$

#### Work Step by Step

Each power supply can be acceptable, having a functional nonconformity, having a cosmetic nonconformity or having a minor nonconformity. Therefore there are $4$ types of power supplies.
Let $a$ be an acceptable power supply.
Let $f$ be a power supply that has a functional nonconformity.
Let $c$ be a power supply that has a cosmetic nonconformity.
Let $m$ be a power supply that has a minor nonconformity.
Hence, the required sample space $S=\{a,f,m,c\}$