Tecnam P2012 Captain reported loss of electrical power during cruise. Captain returned to departure airport and landed safely.

Narrative

This incident began on the previous day when I wrote up the aircraft due to what appeared to be an inoperative right alternator. I consulted with Maintenance regarding my concerns and the abnormal indications observed. Under an electrical load with the tie bus turned off there was a draw/discharge observed from: the Main amps; main bus; Ess. Bus.; refer to AML (Aircraft Maintenance Logbook) log sheet. Maintenance reviewed the write-up and said 'Performed ground run with load as stated by pilot. R/H alternator functions properly. Inspected Act. R/H belt + wiring. No defects noted.'The following morning I conducted a preflight of the plane in accordance to the Normal Procedure outlined in the QRH; reviewed the AML and corrective actions regarding the write-up. The rest of the morning proceeded normally: GPS update day; start-up; run-up; takeoff. Made contact with Approach and continued the IFR flight as planned; Cruise flight 6;000 direct to ZZZZZ intersection. Current weather at 6;000 hard IMC.During the cruise flight; I decided; since I had some time to check to see if the repair worked as intended. I turned off the Tie bus with an electrical load and the draw/discharge was still present. I noted the electrical loads under different tie bus settings; I then left the Tie bus on. Shortly thereafter; I lost all electrical power from: PFD1 (Primary Flight Display); PFD2; MFD (Multi-function Flight Display); Radios; Autopilot; and heaters and etc with no accompanying CAS (Crew Alerting System) messages. In response; I immediately; began hand flying the plane with the compass and standby instruments. I then switched on the Emergency Back up Path Essential Bus". I understand that the emergency essential bus switch bypasses the main bus and connects the main battery and essential bus. I was hoping to regain some functionality of PFD 1 and its associated systems before turning to the QRH.My understanding is that flipping the emergency Essential Bus switch provides an immediate response of electrical power. This was not the case; but I left the switch on nevertheless.With the Emergency Essential Bus switched on I decided to discontinue the flight and returned back to ZZZ airport on a reverse heading knowing that the weather and traffic flow at my destination would have increased variables and associated risk. Once established on a heading back to ZZZ I consulted the QRH and conducted the "Dual Alternator Failure Checklist". It provided no adequate troubleshooting solution; so I continued with my decision and flew back to ZZZ. I then turned the Emergency Essential Bus Switch off and turned on the Main Battery switch; referencing the "Main Battery Failure checklist" in the QRH. The Emergency battery switch connects all three batteries in parallel onto the main bus and is mainly during a dual alternator failure.This also provided no positive feedback as well.At this point; I determined to stop troubleshooting knowing full well that ZZZ airport would be my best option given the following conditions: single pilot hand flying referencing only the standby instrument and compass; while in IMC with a complete electrical failure. I left both emergency switches on at this point with the hopes that maybe one of them would provide power if any. On my descent back towards ZZZ; I exited IMC and was VMC at approximately 2;500' at some unknown distance from ZZZ. Shortly after entering VMC; I regained power to PFD1 and PFD2 and its corresponding equipment (MFD still out). With ZZZ airport was well within sight; I communicated with ZZZ Ops and informed them that I was coming back to land. I committed to the landing and once on the ground I contacted ZZZ Clearance; canceled IFR; stated the reason for the air return was due to a dual alternator failure. Returned to the gate; parked the plane performed all After Landing; securing checklists. Cause: Potential dual alternator failure."