Your s8 device is charged up by a standard ion battery. The galaxy s8 now has a usb-c adapter so the charge that will come in the box is different than the one you used with your s6 or your note 5. Those are usb cables.
Samsung says to not use a 3rd party charging device for the galaxy s8 for your wall charger or your car charger. Those kind of devices can cause problems with your samsung smartphone and actually make your warranty not valid.
Use your usb-c cable that came with the device or one you purchased from an authorized distributor of samsung fast chargers usb type c .