If the 12v laptop adapter you are talking about is a low frequency transformer, ie. a "power brick" then you are likely to be going backwards. Switched mode PSUs are significantly more efficient (less heat to be dissipated), smaller and lighter. If you are converting 240AC to 12VDC with an inefficient low frequency transformer then passing that through the switching pico PSU for 12VDC but converting some to the other rail voltages.... You get the idea. As far as I can see the only real benefits of the Pico PSUs are the small form and the lack of a noisy fan (because you are offloading the heat generation to the laptop brick). I don't see how there are efficiency gains.