What is the general suggestion for PSU used in wet or water environment?

Depending on the installation environment, you may need IP certified power supplies (IP65/IP67). 

Also, waterproof connectors and junction boxes are useful accessories to ensure a reliable operation in damp environments (please refer to the LED power supply installation manual).

Waterproof connector solution

Junction box option

Note that the MEAN WELL product IP level, including IP67, is tested according to IEC 60529. The protection does not guarantee for permanently immersing in the water. Please check the device installation manual for proper suggestions on installation.