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.
If you keep your MRC Loco Motion at or near "full" all the time, then you may get away without a bridge rectifier and the filter cap. Please make sure that the peak voltage (if there's any AC component present in the waveform) does not exceed 24V at any time.
The information regarding this can be found under FAQ -> Troubleshooting -> 02.
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.
The waveform file did not upload, and for some reason the forum will not allow me to upload the file.
You can see all three waveforms at this link, three as bmp files and one also as a PDF:
https://1drv.ms/u/s!AtJVKvMETvjfhqsk9NPRf80a8awRKw?e=7tmlIg