I first saw this practically in the Orthodox Cherokee SMPS. This is where we differentiate from Engineered Products and just Mass Production without following standards. The Cherokee SMPS was a work of art, perfect in all respects.The Copper Desert or Isolation Land
There is a No Man's Land in PCB. Any good power electronics designer should/will know. Product Safety and HV Isolation, Quality and Reliability all depend on this.
High Energy Circuits
These things don't come overnight, it is a culture, learning, experience and integrity of some of these American Firms. Reliability and Product safety are important. Every human values his life very much. A manufacturer too should appreciate this.
Coming back to isolation, Keep in mind creepage distance, High energy circuits and Low voltage circuits should have clear isolation, use the best insulation. Fire and shock hazard. Mains HV transitions, spikes.
Regulated High Voltage Power Supply
Power supply faces all these, even other areas where a Human Life or Property can be endangered.
HV High Voltage Reliability and Safety
Use a Servo Stabilizer or CVT Constant Voltage Transformer or at least an Isolation Transformer. The First Defense form HV Surges, Spikes.
High Voltage Polyester & Polypropylene Metallized Capacitors in Stepdown Supplies should be Fire Retardant & Self Healing with a MOV too.