PA-28 flight instructor reported alerting ATC to electrical system anomalies on their practice approach. The system returned to normal before landing.

Narrative

Student was flying the VOR Z XX into ZZZ Airport. We had departed VFR; but as the clouds were scattered 2600 and it was going to mess with our approach if we wanted to stay VFR; I decided to pick up a pop-up IFR. Student was inbound on the VOR Z XX after completing their parallel entry; and I started to smell a 'dead fish' smell. It was very faint at first; and being completely honest here; I thought the student had passed gas; so I took note of it but did not see it as a problem. As it grew stronger I became more concerned; the student noticed it as well; and all of our electronics shut off for a brief moment. Comms; both G5's; GPS; everything. It flickered back on and then went back off for maybe 10 secs and then came back on. I had taken controls at this time and as we were VFR; so I descended below the upcoming clouds; and started planning for lost comms; but luckily it came on quickly and stayed on. The smell had gone away for the time being. We were already set up on the final approach course for Runway XX into ZZZ so I advised ATC and let them know we needed to land. Approach confirmed it and switched us over to Tower; asked the fuel on board and number of people on board. Ran the checklist; turned off all light and the alternator; and flew it to the runway just below the yellow arc and landed without incident. Fire trucks were waiting for us and we shutdown. As for if it happened again; if we lost comms and they had stayed off; ZZZ1 airport would have been my first option. But with comms back and being able to get the call through; ZZZ airport has more services if the worst came to worst and we were already set up on the final approach course. Even thought the smell went away and everything came back on; I definitely made the correct decision to advise ATC; but I think it's good to think over the scenario and evaluate how I would react to it next time.