Per the common product safety standards (national standards based on IEC 60950-1, 60335-x, 62368-x), Class I and Class II construction are defined per the level

Per the common product safety standards (national standards based on IEC 60950-1, 60335-x, 62368-x), Class I and Class II construction are defined per the level and type of protection from shock for 'grounded' and floating enclosures, respectively. Per your SMPS reference, the output reference depends on the design intent and intended end-use environment. Depending on the scoped standard, outputs greater than 50Vdc will require a minimum separation from the both exposed dead metal and stuff referenced to an earthing terminal. Where the output is considered safe to to touch, there are only functional spacings required. Also, Class II construction is, in fact, not intended to be 'grounded', and must not be a hazard for a fault condition where the enclosure touches either mains voltage or metal referenced to an earthing terminal. Class II construction requirements are supposed to mitigate a single fault condition associated with seperation from and contact with a hazardous voltage or power source. Most potentials between the user and ground are due to current flow through the y caps (noise filter caps rated to between a hazardous voltage level and the user). Touch current, depending on the scoped standard and category and class of equipment is typically limited to less to 5mA (some equipment is allowed 25mA). Class II equipment is typically limited to 250uA. Given the assumed human-body models in IEC60990, the voltage at max allowed current leakage would range from imperceptible to noticable but not effectual. Shock hazards can exist from improper construction or improper installation and of equipment.