When I was growing up in DC we had "street cars" that ran off a 600VDC "plow" that picked up the power from an underground rail. GM conspired withe O. Roy Chalk, the owner of DC Transit, to rip them out and replace them with GM diesel buses. He got the first bunch of buses for free if it would rip out the street car tracks.
There is quite a variety of weir bus mutations out there and so far none of the systems fared particularly well. The original trolley bus system is nothing but a bus with an electric motor and a 2 wire overhead line. This combines the disadvantages of a rail system (not much ability to evade obstacles, maintenance cost of the overhead wires) with those of a Diesel/gas bus (less comfortable ride for the passengers, equipment and operators, damage to the street surface due to the heavy vehicles, large bend radii).
The there have been several tries to improve those systems by keeping th bus on track, either by adding a center rail keeping the bus in line or by uing "virtual rails", an electronic positioning system. The first system failed catastrophically in several French cities, with frequent derailments and horribly bumpy rides. It simply did not work. The latter system never made it past the project stages I think.
Urban transit systems usually operate on 500-900VDC with very few exceptions (some German streetcars run off the 15kV 16.7Hz railway supply and can run on regular railway lines too, in Vienna loooong ago we had a 750V 16 2/3 Hz system, the cars could operate on DC too, inside Vienna they ran off 600VDC, outside (25km to the nearby town of Baden) on AC).
Ahh Sandro I remember those electric buses we had in Hamilton as well! I think my Dad said those things ran at 600V D.C and if I am not mistaken the supply for all those was down on Kennilworth Ave North...
I can remember being a little kid and riding with my parents on the trolley to my aunt's house in the west part of the city once a month for Sunday Dinner. Every time we went over a crossing in the wires the bus would slow down and the interior lights go out for a second or two.
From what I found on the internet Winnipeg Transit got rid of its last trolley bus at the end of October 1970 and sold all but one of them to Mexico City. They only had 6 trolley routes in service by 1968 and were down to the last one in 1970. The suburbs to downtown were already served by diesel buses starting back in the 1950's.
The Manitoba Hydro electrical museum has on display a 1950's era glass bulb mercury arc rectifier used to convert ac to dc for the operation of the transit trolley buses. I can still remember seeing the bright light coming out of the trolley substation buildings and wondering what was causing it.
I know that New Flyer here in Winnipeg still builds trolley buses as well as diesel buses.
According to the New Flyer web site in 2005 they delivered an order to Vancouver BC. These buses have a small UPS to allow them to go off the overhead grid for short periods to get around closed streets due to watermain breaks, fires, accidents, etc.
The lack of street flexibility was always a big knock against the trolleys according to my uncle who was a Winnipeg transit supervisor.