On TurboCharging, "Charging Slowly" message displayed on my phone Moto G4 Plus My Moto G4 Plus has the turbo Charging(30 min Charge 80%) feature.
 But when I connect to a Turbocharger, I get a display message on my
 lock screen as "Charging Slowly".  On connecting a general charger
 Phone charges as usual in 3 hrs. I am curious to know, with only the
 given knowledge, how can I predict whether the issue is in Mobile
 Phone Hardware or Software or the specific Turbo Charger.
Moto phones are quite close to Nexus phones or pure android as commonly referred to, so the explanation below is valid
See Android phone &quot;charging slowly&quot;: How to make it faster, for reasons on why charging slowly is displayed, in particular Andrew's excellent answer. To summarise, fast charging/ Turbo charging is achieved by increasing voltage or current or both, i.e. wattage ( being the product of current and voltage), as compared to conventional charging. Andrew's answer explains the values for which such notification appears ( Nexus phone on linked question uses a different type of which charging compared to your device, but that is a minor detail, since OS is flashing the notification based on wattage values and not on type of quick charging)
So, the most likely cause IMO, is that your Turbo charger is not working well or it is not receiving adequate voltage ( connect through a voltage stabiliser, avoiding extension boxes). You can verify otherwise by going to service centre and checking with the Turbo charger sample. 


Do revert with your findings

Edit: I own Moto X Play and the charging cable is fused with the charger. If your charging cable can be detached from charger, try replacing with a good charging cable, to eliminate cable issue