In many of the cases the drivers were prevented from using their vehicles because the condition was so poor.
The night-time operation focused on vehicles taking people in and out of the city centre.
Four were seized for serious defects, three for no insurance and 11 fines were handed out for minor offences.
The operation was carried out by South Wales Police, VOSA, HMRC and Swansea council.
More than half of minibuses, taxis and private hire vehicles checked during a two-day clampdown in Swansea were found to be unsafe.