Dell Inspiron 5160, power adapter randomly turns off

Hi,

I've got a problem, my power adapter will turn off randomly sometimes, and I don't know why, I called Dell and they've sent me a new one, and this one does the same thing too, for example, I leave my computer I come back, I notice that my computer is working on battaries, cables are plugged it tight, but adapter's light is off, and to make it work again, I have to disconnect the cable from the adapter's "brick" then from the outlet, connect to the outlet again and then to the brick, and it lights up again. It won't power on if I only disconnect it from outlet and reconnect it, dunno why but it starts working only when I disconnect it from the brick too, and it doesn't matter if it's plugged into the laptop or not. It's too bad I haven't actually witnessed how this happens, cause it happens randomly, sometimes days pass without this occuring.

Does anyone know what could be the problem?