If a perpetrator needed to bring light to just inside Meredith's door, why would he unplug Amanda's lamp and bring it into Meredith's room where they then need to find an outlet and unplug Meredith's computer to plug it in. They would instead just grab the lamp, turn it on and walk into Meredith's room with it*.
The only reasonable explanation for the state we find it in is that the person borrowing the lamp either didn't want to leave the extension cord draped across the hallway (ie: Meredith using it 1 or 2 nights earlier) or they needed to minimally disturb the evidence* (ie: early police on the scene needing more light).
(* See for evidence the extension cord which was plugged into Amanda's outlet by her door with the other end behind the box next to her desk)