Glad to hear you had some "Non~Destructive " testing and all went well!
The Train set Variable supply IS a good Idea EXCEPT .. be sure of 2 things..One it has enough current to test with..(amps not milliamp) and IT IS NOT A.C voltage! AC voltage WILL Destroy any Solid state devices on the line..
Linear, CMOS/HMOS technology will not tolerate ANY AC on a DC source line..The chips will go into Thermal shutdown ( usually forever) and the unit will be destroyed. (ECM's, ECU's, Alarm systems, Tach, Digital Dash, CD players, power amps,Digital clocks)
This is why I Never advocate using a battery charger for testing new harness. Chargers ARE not Regulated, Nor Well Filtered..a Standard wally~mart charger usually consists of a half wave rectifier, a Filter cap, multi tap transformer, and a Current meter and fuse..
This means each half wave of AC power that passes from the transformer, will pass through to the DC side, and cause an AC ripple (or wave form) that can be destructive..
A Bench supply, (used for DC testing) HAS a full wave rectifier , AND current and Voltage regulation, surge and spike suppression, proper fusing and A CLEAN DC output.. Unfortunately not everybody has one..
If you would like to test the theory, hook any OLD car radio up to a battery charger and SEE what you get...IF it works at all, you will hear nothing but an intolerable buzz..in the audio output.
I always advocate the use of the lantern battery's, if no bench supply is not available.
Anyway..It's good to hear you had success..
Onward and upward!