Attempts like this have been made in several European countries around 1900, but this is the only one I ever saw a clear picture of, and probably the only one that has been in service for such a long period of time.
Having two pantographs up is usually avoided here out of fear the power line might start to oscillate and damage the second pantograph.
Traction voltages are a nightmare around Europe... I think anything from 500-3000V DC and 1500V-25000V AC at 16 2/3 and 50 Hz are currently used. Take Austria alone... Vienna streetcar (tram) is 650V DC overhead supply. Vienna Subway is 750V DC 3rd rail (4 lines) or overhead (1 line). Suburban light rail to Baden (streetcar-like local railway) is inside Vienna on 650V tram supply, for a short section of track on 750V subway and on it's own track outside Vienna on 950V DC. The cars are quite lame inside Vienna...
Long-distance service is solely 15000V @16.7 Hz (nominal, actually it's a rounded 16 2/3 Hz), whereas smaller local lines often operate on 1200 or 1500 V DC overhead. German and Swiss long distance are the same as Austria (not sure about Switzerland), so that's not such a big problem. Hungary is 25000V 50 Hz though, System #2. Italy is 1500 or 3000V DC. Don't know about Czech Republic, Slovakia and Slovenia.
The old Vienna metro (until 1983) had trains of up to nine short 2-axle cars, multi-unit operation with three motorcars! Built in 154-1961, using most of the mechanical parts from the old 1925 cars, boosting a maximum speed of 40km per hour...
