How do I make a Waterproof Power Connection?

A pollen sensor runs off of household power (110v US/220v EU) that is connected to a 12v DC adapter. That connection from household power is typically made by running an outdoor-rated extension cord to the power supply. Their connection needs to be waterproof and a special enclosure is often used.

The example below is not one we’ve tested but serves to illustrate the kind of product that is capable of waterproofing the connection.