Using indoor only power adapter outside
Those waterproof covers are only rainproof. They are open at the bottom for the cords to go through so they are not moisture and humidity proof. Outdoor rated cords have a heavier, much heavier, insulation to protect them from the outdoor environment, sun, UV, animals,etc. The male and female ends are also insulated heavier and are of higher quality. Connecting to a weatherproof box is not the same as indoor use and if the outlet is outdoors, it will have to be GFCI protected.