True instant sync via Dropbox
AFAIK, true instant sync (as in first para of your question) , isn't possible using Dropbox, for reasons mentioned in answer here. If Dropbox itself doesn't permit, you can't force it through either apps you tried (I tried and have the pro version of both these apps).

My need was to have a real time sync across Android and PC (Linux and Windows). The only app I could find was from standard notes. The Android app on Play Store is marked beta but don't let that discourage you. It works perfectly well on Android, Linux and Windows for real time sync.

Only thing left is Dropbox sync - if you go in for pro version of standard notes, you can install an extension, that provides daily updates to Dropbox, and obviously isn't real time. But then your files are synced across platform in real time, so updation in Dropbox may not really matter, unless you have other reasons. I haven't tried this extension because I stopped using Dropbox.


As far as real time sync goes this ticks all the boxes except via Dropbox. You don't need to go in for extended (pro) version, if you decide to cut off Dropbox or use either of the apps you tried for periodic sync.