I have an ASTEC (Model MP4-1E-1L-1Q-1W-0M) 12V switching 400W power supply
Well good for you! These monster power supplies were quite popular about the middle of the previous century when digital electronics equipment required a multiplicity of voltages at moderately high currents. In Dayton, OH, the National Cash Register Corporation surplussed dozens of similar models, which were immediately snapped up by a local salvage and surplus dealer. I was working for the University of Dayton Research Institute as an electronics technician at the time when NCR (which occupied vast areas of soon-to-be-abandoned property next door) invited us over to inspect and take whatever we wanted. I noticed the power supplies mounted in relay rack cabinets, dozens of them in this one building, but what I also noticed was a large, chest-high, steel cabinet with a static Hollerith card reader mounted on top. So, I took that puppy and left the power supplies for someone else.
On a somewhat hysterical (historical?) note, the building, before its exterior was extensively remodeled, was originally used by a cadre of women "code breakers" who were boarded in strict isolation at nearby Sugar Camp during WWII. When word got out that the building was to be razed, along with most of the other NCR buildings, a protest movement to preserve this "historical" edifice sprung up. But money talks and bullsh!t walks, so after a brief flurry of activity one day the building simply disappeared! Today, the University of Dayton owns most (if not all) of the former NCR property, including the former NCR headquarters building which the Research Institute now occupies.
Obviously the Astec is waaay overkill for your model railroad application.
I suggest that you consider using a sealed lead-acid (SLA) 12 VDC battery of the type used in emergency lighting and UPS units. Connect it to a "float" or "trickle charger" as your power source. It should provide plenty of power for a few hours of model railroading activity and then it will replenish the charge overnight.
Or try to remove the lamination buzz from your existing power supply. I know how annoying that can be, but maybe you could just put the power supply, maybe suspension spring mounted, inside a sound-proof box, maybe with a quiet, low-speed, muffin fan added to the box for ventilation... Happy Railroading!