From the question it sounds as if you're talking about the charging cords (with the voltage transformer blocks) being plugged in, but the cell phone, computer, etc. not connected to the charging cords. In this scenario the answer is no, they do not consume any electricity. You can verify this by touching the transformer block after you've disconnected the cell phone or computer from the charging cord and waiting an hour or so. The block should be no warmer than room temperature. This is not necessarily the case with charging platforms that allow you to wirelessly charge up cell phones, etc. by just placing them on top of the platform. These will probably consume a small amount of electricity as long as they are plugged in, and of course much more when you place a cell phone on top of them, at which point the charging circuitry becomes active.