It won't work. You will likely ruin the device you are plugging it into. You have to provide the right voltage or you will burn out one or more components in the receiving device. Voltage is a measure of potential energy. If you deliver 19V to an electrical circuit expecting 5V some of the parts (resistors or transistors, etc.) will get too much energy, then get too hot, and burn up. You might even see some smoke. I would not try it unless you don't care about the 5V device you are going to fry. The adaptor will not lower its voltage to accommodate the receiving device. By the way, you also have to be careful of the polarity. The + or the - sign. Most of this you can learn by asking a salesman at a store like Radio Shack or The Source.