Samsung's Galaxy S8 and Galaxy S8 Plus, specifically the Qualcomm Snapdragon 835 versions deployed in the United States, seem to be having problems with charging after a recent update. The update in question seems to be the October security patch, and many users are reporting that the update has caused their Galaxy S8 and Galaxy S8 Plus units to either no longer fast-charge, or no longer charge via the USB Type-C port at all. Some users reporting the latter are also saying that their phones are charging slowly when charged wirelessly. Wireless charging is usually a bit slower even than charging with a generic cord and adapter, and no users seem to be reporting such an issue with Samsung's fast wireless chargers. Additionally, some users are reporting fast battery drain following the installation of the new software package. Samsung has yet to make any official comments on the matter.
It's worth noting in this case that no other Samsung phones seem to be having the same issue. The Galaxy Note 8, which is based on the same chipset, has been reported having some charging issues, but they don't seem to be connected to the October update. The international versions of all three phones based on Samsung's own Exynos chipset rather than the Snapdragon 835 also seem largely unaffected. Since it's almost December, the November patch should be coming soon and should hopefully help with this issue.
This is far from the first time that a Samsung update has seemingly caused problems with one of its devices. Not too long ago, owners of certain Samsung Smart TVs in some territories got an update that made their televisions almost completely unusable, even for non-smart functions like playing video games over HDMI or watching cable TV broadcasts. Thankfully, these sorts of problems are fairly rare and generally tend not to happen more than once to a given device during its life cycle when it comes to Samsung. Samsung has recently been improving its software support practices as even the Galaxy S6 now seems to be in line to get a major update to Android 8.0 Oreo after its end-of-life date.