Interesting you should mention QSI. I have an On30 BLI C16 2-8-0 which has a QSI circuit board and the parallels are obvious.
It runs on DCC or 12v DC, automatically detecting and setting itself. I use it with various transformers, including a Hornby unit dating from the 1980s, and it runs just fine on all of them.
It doesn’t have the reverser or neutral function in either mode, just forward or backward from the controller. In 12v DC, it goes through a start-up sequence of “engine sounds” up to about 3v, then moves off at about 5v. Flick the power to OFF momentarily, gives you the whistle; flick the power past OFF or flick the reversing switch, gives you the bell - which all sounds very like the Lionel style whistle and bell controls. It has no battery or BCR.
It’s a nicely thought-out system which works well.
Regarding circuit breakers, bring in the U.K. I have a two-stage reduction - 230v AC to 110v AC, then a KW to give 20v AC. I presently use a proprietary step-down transformer bought on eBay for the primary step-down, and I find that this will trip out before the KW; which I suppose, illustrates your point about modern electronics being more sensitive.
