A lot of people are saying resetting the phone worked for them. You don't have to reset your phone and lose all of your content, settings, etc. I narrowed the problem down to either the charging port in the phone or the cord. My issue ended up being the original charging cord that came with the phone itself. I went to Best Buy, bought a new USB-C cord. I had the gentleman plug it up to make sure it worked before I purchased it. It worked perfectly. It cost me about $25 to get a braided cord that is more sturdy, and will last a long time.
I've had the S8+ for 13 months now. I have gone through this mess 4 times in that time. This is actually the second S8+ device I've had in the past year (this is a replacement for the original that was damaged.) I have used a vast assortment of chargers and cords with these devices. I have tried the "just flip the connector over and the problem is solved" trick. After a while it gets to the point that unplugging, replugging, flipping it over, standing on your head while letting the neighbors gerbil in a thunderstorm at midnight will not solve the problem. At that point the only option that I've found that actually works is doing a factory reset. I've had to do this FOUR times in 13 months. On a phone I paid roughly $1,000 for. And nobody at Verizon, AT&T, or Samsung has ever heard one single word about this issue. I am always the very first person to ever mention it to them.
The new Pixel 3 comes out in about a week. This is my 6th and last Samsung phone.
I found that the connection is incomplete. This might be because it's dirty connection. In my case I noticed my cord was pretty narrow and wondered around in the port. I took a tool and squeezed the wide side to widen the opening of the center. So it would have a better connection with the negitive connection to the outter metal from the cord to the port. I found the charge time remained steady even when wiggling the cord a bit. Granted the time changes after a few seconds after plugging it in but after that is what I'm talking about.
So this happened to my note 9 right out of the box. I had a Qualcomm quick charger from my old htc10, plugged the Samsung cord into the Qualcomm brick, and immediately charged quickly with no problems. So either Samsung's bricks are broke af, or they just really suck. This isn't much of a solution, I know, but they sell those same bricks on Amazon for those willing to spend the same amount you would for a Samsung charger for a charger that actually works.
Same poblem here. I know this isn't an answer, but it worked for me. I got one on those metal dental tools for scraping tarter or plaque off your teeth. Cleaned out all around the pins on the port on the bottom of my s8. Way down deep. I powered off before just in case. I had a big magnifying glass and could see lint or something in there. Blew it out with canned air. Now connects and fast charging on all cords, all chargers, including the vehicle. I hope this helps.
My experience with the incomplete connection issue is that it is CABLE related. This occurs for me with certain charging cables, particularly 3rd party cables. It will also sometimes occur when using a mimi USB -> USB C adapter. Frequently the message disappears if I unplug cable from phone and reattach.