gateway NV53A power supply help

my gateway nv53a is plugged into the power supply everything works fine desktop icons shows that its connected to an outlet and laptop work normally, after awhile of using laptop (plugged in) 20 - 30 mins its all a sudden switches to to using the battery the icon no long says its plugged in even tho it is, even replugging it back in (even on diff wall socket) will it switch back to useing plug. ok does this sound like power supply is going bad? it doesnt feel overly hot when it does it. the powsu charges battery like it should,  basically wondering if this sounds like bad powsu or  Circuit in laptop for switching between the two

    thanks chan