Note the proposed DC control modules (whether the LM317 type, the PWM type, etc.) can only LOWER the effective output voltage. I'd think starting from 12V DC as from a PC power supply should be enough for trolleys. If not (i.e., you need more DC voltage) another source of low cost DC power might be a 90W laptop charger. I have written about this in other threads but here's a couple relevant photos:
These go for between $5-10 shipped on eBay (search for 90W Universal laptop charger). This one has a selector slide switch to change the output voltage from 12 to 24V DC in 7 steps with LED selection indicator. There are other wattage converters of course but I thought 90W was similar to your 75W Z brick.
A side-by-side with the AC output Z-1000 brick. Note not just the size but the physical weight difference!
In any event, if you go the DC route, definitely consider the PWM motor controllers as Shorling shows. The point being DC voltage controllers are more readily available and inexpensive that AC voltage controllers.
