I saw a note somewhere on this site that LocoFi would not work with pulsating DC. I assume that means it will not work with an MRC Loco-Motion 1500 power pack, since it has a pulsating DC waveform for all settings other than 0% and 100%. At 0% the voltage ism zero, and at 100% the voltage is a virtually constant 18 to 19 Volts. But between 0% and 100% the waveform is a combination of a variable DC value and a ~ 18 volt pulse. See the attached waveform for the 50% power setting. 0 is in the middle of the screen.
Locofi recommended using bridge rectifier https://www.amazon.com/gp/product/B08JM5XQQW/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1 and a capacitor https://www.amazon.com/gp/product/B07M8PJKGJ/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 my Locofi equipped engine ran fine after i added these betreen my power source and the rails.