The Dell X639C AC adapter supplies power to Dell laptops. The model number identifies this specific adapter when comparing it with other Dell power supplies.
It is rated at 90 W and 19.5 V, describing its power output and voltage for laptop operation. This is a separate power adapter, not a laptop component.
The laptop-side connection is a 7.4 mm connector. On the power side, this version has a 3-pin plug and is specified with a C6 power cord. These details help identify the connections when checking whether the adapter matches a setup.
Its documented specifications are 90 W, 19.5 V and a 7.4 mm connector; X639C identifies the particular model.