The water-resistant Galaxy S7 and S7 edge feature a moisture sensor in the USB port
Given that the Samsung Galaxy S7 and the Galaxy S7 edge both feature IP68-certified water resistance, it's not surprising that Samsung warns about drying up the USB port of wet phones before feeding them electrical current. The Galaxy S7 edge user manual reads:
However, it was recently discovered that Samsung went beyond issuing a warning. The Samsung Galaxy S7 and the Galaxy S7 edge come with a special moisture sensor that prevents the phones from charging when humidity is detected in the charging port. If you'll try to charge it right after giving it a bath, the phone will pop an adequate message and refuse to charge.
Interestingly, some early users say that this humidity sensor is actually so sensitive that third-party charging cables that do not adhere to Samsung's specifications can accidentally trip the warning.