The quick answer is no, you cannot mix regular antifreeze with Dex-Cool. They are two different types of coolant, and mixing them can cause serious problems.
Dex-Cool is a newer type of coolant that was developed by GM in the 1990s. It is made from organic chemicals and is designed to last longer than traditional antifreeze. Dex-Cool also has a lower freezing point and a higher boiling point than regular antifreeze, which makes it better at protecting your engine in extreme temperatures.
However, Dex-Cool is not compatible with traditional antifreeze. If you mix the two types of coolant, it can cause corrosion and deposits to form on your engine parts. This can lead to engine damage and overheating. So if you have Dex-Cool in your car, be sure to use only Dex-Cool when topping off the fluid levels.