Nothing wrong with using a non-toy train 18v transformer as long as it is an isolation transformer - i.e. the secondary coil is not electrically connected to the primary. The MPI transformer datasheet shows it is an isolation transformer. Many of the transformers I have tried to salvage from power supplies are autotransformers where the primary and secondary share the same wire (different taps from the coil provides voltage reduction). This is a safety issue as it ties the track to the house wiring.
I use variable transformers (Variac is the trade name) ahead of the 18v transformer to adjust the output voltage. Note that all the variable transformers I have found are autotransformers so never connect one directly to the track.
My 18v power transformers are Hammond 165 series "filament" transformers. Available in 10, 15, and 20 amp output at 18v, part numbers 165S18, 165U18, and 165V18 respectively. Considering today's pricing and the need for additional parts (breakers, enclosures, etc.) to incorporate these into a layout, the PH180s may be more cost effective.
My circuit breakers are 10A instant trip.
