First,
Try to soft-reset your phone (harmless, like rebooting a computer). Preferably without any SIM or SD cards installed.
Second,
Try a different charger, preferably one which you can confirm works perfectly with another device. The charger you tried before could have a dead AC adapter or a broken cable. The connector on the cable (which you plug into the phone) might be damaged, ensure there are no bent/missing pins, dirt/debris or other obstructions which prevent proper electrical contact.
Check the charge port on the phone itself. Again, make sure there are no bent/missing pins, dirt/debris or other obstructions which prevent proper electrical contact.
You can carefully clean these connectors with a Q-Tip and electrical contact cleaner (DeoxIT, stabilant-22, or even isopropyl alcohol). You can carefully pry things out or bend them back into shape with tweezers. You can also snap fragile metal bits or break the connector with tweezers. Unplug power and disconnect/remove battery before poking anything electrical, of course.
Third,
If nothing above fixes the problem, try to hard-reset your phone (a hard-reset will delete all user data on the phone, so backup or copy whatever you need to save first, if you can). You could just do this first (instead of the soft-reset) if you don't at all care about preserving any data which might be stored on the phone.
Finally,
At this point you know that the charger works and has proper electrical contact, and you know that the phone's firmware or software hasn't crashed or gone buggy. I assume you'll know the AC wall receptacle has power. So if the phone still won't accept charge it's because of a hardware problem in the device, likely because the battery is shot or a charging circuit/module or an internal power connector between them is faulty. Yes it's possibly something bad on the mainboard. It's even possible that some other conductive part is where it shouldn't be and you have an open (short) circuit or ground fault somewhere in circuit before power reaches the mainboard. I've seen dead devices resurrected by simply reseating the battery after the flimsy metal contact tabs were somehow knocked out of contact.
This site has detailed repair guides and sells the parts (and tools) you might need including new battery, Power Button Cable, charge port, and battery connector (these last two parts require PCB soldering/rework). The SM-G920FD and SM-G920F have nearly identical specs (aside from number of SIM card mounts) but I don't know if their mainboards are interchangeable or have intercompatible form factors. Unique device identifiers like the IMEI (along with carrier lock, lost/stolen blacklist, etc) are encoded on the mainboard, so you'd effectively be using the entire SM-G920F phone in a (single SIM) SM-G920FD case - and if the SM-G920F already works fine then it hardly seems worth the effort unless your SM-G920F is otherwise damaged.
If you've installed (or attempted to install) modded firmware or if your mainboard is bricked then all bets are off, lol.
