The current stated on the sticker is more of a theoretical maximum that it would draw, it'll usually draw nowhere near that. The best thing to do is just get one of those cheap plug in power meters and use it to get a proper measurement. Also bear in mind that the amount of power that it draws will vary based on how much load is on it, you'll pull a fair bit more power when the machine is doing something computationally intensive compared to when it is sitting at idle.