Outdoor receptacles (outlets) that do not have "in-use" or "in-service" waterproof hooded covers are not meant to accommodate plugs and cords on a permanent basis. If a person thinks about it, the reason is obvious. Water, from rain or watering a garden, can get into the receptacle and water and electricity do not mix well. The photo below would be an example of the problem inspectors often see. So what are those cords? It is hard to tell but they usually go to some yard feature -- a pond, a fountain, a timer, maybe low-voltage yard lights. 

I know this arrangement does not hold up to moisture. Years ago, my wife was watering the garden and she killed a GFCI receptacle that was supplying power to a pump at my pond. Do not get me wrong, I agree that the cover above is intended for outside use -- but not when cords are left in place. That condition exposes the receptacles to the elements. These covers are made for periodic use: Plug in the weed-eater, when you are done with it, unplug it from the receptacle and close the waterproof cover.

When I tell clients that there are "in-use" waterproof covers, designed for just this purpose, they often do not know what I am talking about. The hooded covers are common and they are available at hardware stores or home stores. Like most consumer products today, they come in various styles and sizes to accommodate a number of different receptacles. The one pictured below is made for two side-by-side receptacles. The best part of the equation is that these covers are waterproof and "in-service" come rain or shine.

Steven L. Smith