Commercial Cessna 404 pilot reported an alternator failure and received priority handling from ATC.

Narrative

Had an uneventful preflight; run-up; takeoff; climb and cruise. About an hour in I noticed a shower of sparks come from the left engine between the nacelle and spinner. I caught the first sparks out of the corner of my eye; and after a moment a second shower of sparks come from the same place. These sparks were concurrent with a flickering L ALT annunciation; and as I recall; the annunciation was only present along with the sparks. I knew the aircraft had undergone maintenance to this alternator; so I determined this to either be a shorting wire or some internal issue with the alternator. As soon as I determined the alternator to be the issue; I turned the switch off and attempted to pull the CB (Circuit Breaker) with no success; but the sparks never reappeared after that. At this point I requested priority handling and pointed the plane back towards base at ZZZ; keeping a close eye on all engine instruments and planning for an emergency landing at a closer airport to our imaging location. The L ALT annunciation reappeared with the alternator switch off and remained that way for the rest of the flight. The sparks never reappeared and the rest of the flight stayed relatively uneventful. Emergency services were rolled out at ZZZ; but there was no indication of a fire; only that there was an electrical burning smell from the cowling.