This problem just started yesterday (8/31/17) with my Galaxy S8 plus. The message shows up when I use the wall adapter that came with the phone. It works fine with the car charger.
I have not tried anything to fix it yet.
** UPDATE TO THE ORIGINAL POST ** (by userdE8nbUMBRW)
I contacted Samsung and after speaking with a technician, they diagnosed the problem with the wall charger/cord that came with the phone. This occurred during a single phone call. I sent the faulty products back to them and they sent me new ones. No hassles at all. I have been using the new wall charger/cord for about a week now, and it's working perfectly. I suggest everyone having the same problems do this.
I am and have been encountering the same issue with my Galaxy S8. I have used nothing but the wall charger provided by Samsung with the phone. It slows charging and constantly pops up stating an incomplete connection. The charge time has slowed significantly since it has an "incomplete connection". Model Number is SM-G950U and Baseband Version G950USQU1AQGL. This is very disappointing as I have been very excited for this phone and I paid for it in full and now it is not performing up to par.
My brand new Note 8 gives this same error after being only 1 week old. I am always careful plugging it in. This happens with the home charger that was provided when I received the phone. Odd thing is it only happens on one side. If I flip the terminal over, no error. Seems that Samsung didn't perfect the two sided cable before rolling it out. Very annoying for a phone that is suppose to win people back after the Note 7 ordeal.
Brand new note8. I switched from adapter to cord provided and it's charging now but the error is still there even after powering off and back on. At least its charging but worried about the connectivity error that won't go away. Just knew the note 8 would be great after note7 fiasco. I was wrong after just a few weeks of owning the phone...wow.
I purchased a Samsung S8 less than a month ago and I'm also experiencing the same "incomplete connection message" while using the USB cable and block i got with the phone.
I too have this issue. Purchased phone in July at our local Verizon store. When using the included power cord/wall charger tells me incomplete connection. When using car charger i purchased separately works just fine. Had one day issue 2 system updates ago. Rebooted phone and it went away. Did this last system update now have issue everytime I use wall charger included in box. Screen shot of baseversion attached.