At least as recently as 2007, most of the substations powering Wellington's trolley buses used mercury arc rectifiers.

See page 138 onwards of this document:

http://uat.vector.co.nz/sites/uat.vector.co.nz/files/DISCLO~1_0.PDF

5.12. DC SYSTEM
5.12.1. ASSET DESCRIPTION
Vector provides a 550V DC supply to the trolley buses in Wellington. This supply
originates from 15 distributed substations, containing 15 converter transformers,
19 mercury arc rectifiers, 2 solid state rectifiers and 53 DC circuit breakers. To
provide backup supply, in case of faults, there is approximately 53 km of DC
underground cables linking the substations.