Why do wall mount power supplies only meet Class II power?

Most wall plug in external Power Supplies are designed with only two input conductors (line and neutral) so the Power Supply can be plugged in either direction in a wall or power strip socket. The dc output voltage of these supplies is floating relative to ground since ac safety ground is not present at the input.

Shenzhenshi Zhenhuan Electronic Co.,Ltd(www.szzhpower.com) was founded in 2008, specialize in external power adaptor, ac dc adapter, Outdoor Waterproof power supply, led driver , Power Transformer, switching power supply, dimmable or non-dimmable LED Drivers and Battery Charger in Shenzhen, China. 

Zhenhuan is one high quality power supply manufacturer, we also have own brand  KSPOWER, and our products of power range from output 4.2W to 384W (output voltage 4.2V to 48V, output current 0.2A to 20A) a total of 1000 kinds of models and come with safety regulation standards: IEC/EN 62368 60950, IEC/EN 61558, IEC/EN 61347, UL/cUL 62368 60950, UL/cUL ETL/cETL 8750, UL/cUL1310 CLASS 2 and in full compliance with UL/cUL ETL/cETL RU/cRU CE ROHS SAA C-TICK KC KCC GS TUV FCC CB NOM CCC PSE CB certifications for global markets.