Your hot adapter is due to a couple reasons. Videos can be very power intensive for a laptop. So the laptop is drawing more power than if you are doing email. This is especially true for laptops that do not have a separate graphics card. More importantly the extension cord will cause the voltage to drop some before reaching the power adapter. This will result in a higher current to the adapter and greater heat build up. I would guess that this is a replacement adapter and is of lower quality than a original replacement. I would avoid the extension cord or get an original replacement from Dell.