It is safety standard certification. We also called it as SAFETY in short form. There are different standards of switching power supply safety approvals and every country requires different standard of safety. Safety also has different types for example USA is using UL, Canada is using CSA and TUV, VDE are used in Europe, other than  these are CB is used in Australia, US and European markets, China is using CCC. Manufacture will have label of safety stick on the each power supply enclosure for customers reference and to avoid forge. Simply speaking, safety test is in normal and is not normal (any situation) the behavior in service down uses this product to test if cause the damage to the human body (for example leakage or detonation and so on). Because power source in use time can produce the heat generation P/S design is not only can create the system the injury but also cause series damage to human bodies.