Typical laptop, and AFAIK, all Dell's too, have a switching power supply "brick" that outputs in the 12-18V range. That goes to a power board internal to the notebook, which is another switching-regulator type that reduces voltage to 3.3V, 5V, and other specific voltages dictated by specific components/design of laptop.
So, it's kinda like a PC power supply except that half of it is internal to the laptop. This also makes it easier to power via alternate external power sources, providing you know the voltage range the power board will accept.