'''This sounds like your AC outlet is incorrectly wired!''' Get an outlet checker to verify your outlet is properly wired [https://www.homedepot.com/p/Receptacle-Tester-400-029/206303234|Receptacle Tester]
I'm suspecting your common and hot wires are reversed!
That is when the '''Common''' White wire is going to the Brass screw instead of the correct location which is the Chrome screw! And the '''Hot''' Black wire is going the Chrome screw, when it needs to be on the Brass screw!
So when you plugged in your mini you shorted out between the Hot and Ground! (Wired with Common in the breaker panel) Bang! A puff of smoke and melted plastic.
=== Update (08/07/2020) ===
At this point it you’ll need to replace the power supply and hope that takes care of it.
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Here’s the needed part [https://www.ifixit.com/Store/Mac/Mac-mini-A1347-Late-2012-Late-2014-Power-Supply/IF171-017?o=1] and here’s the guide to put it in [https://www.ifixit.com/Guide/Mac+mini+Late+2012+Power+Supply+Replacement/11722]
'''This sounds like your AC outlet is incorrectly wired!''' Get an outlet checker to verify your outlet is properly wired [https://www.homedepot.com/p/Receptacle-Tester-400-029/206303234|Receptacle Tester]
I'm suspecting your common and hot wires are reversed!
That is when the '''Common''' White wire is going to the Brass screw instead of the correct location which is the Chrome screw! And the '''Hot''' Black wire is going the Chrome screw, when it needs to be on the Brass screw!
So when you plugged in your mini you shorted out between the Hot and Ground! (Wired with Common in the breaker panel) Bang! A puff of smoke and melted plastic.
+
+
=== Update (08/07/2020) ===
+
At this point it you’ll need to replace the power supply and hope that takes care of it.
Lets back up for a sec ...
'''This sounds like your AC outlet is incorrectly wired!''' Get an outlet checker to verify your outlet is properly wired [https://www.homedepot.com/p/Receptacle-Tester-400-029/206303234|Receptacle Tester]
I'm suspecting your common and hot wires are reversed!
That is when the '''Common''' White wire is going to the Brass screw instead of the correct location which is the Chrome screw! And the '''Hot''' Black wire is going the Chrome screw, when it needs to be on the Brass screw!
So when you plugged in your mini you shorted out between the Hot and Ground! (Wired with Common in the breaker panel) Bang! A puff of smoke and melted plastic.