For what it's worth:
About 22 years ago, I was climbing through 3000 in a 152 out of Lydd, with a student on his second or third lesson. He was also one of my first students. Very suddenly, when almost 4 miles from the field, the power reduced to 1850/1900rpm despite a wide open throttle. Since I had control at the time, I lowered the nose and turned towards the field, re-assuring the student that we could easily glide to the field whatever happened. No adjustment of anything gained me anymore rpm. An easy controlled descent to a tight base join got us in without any issue. Once parked, accompanied by the rescue boys, we got the engineer out. One of the two plain bearings (bronze I think) in the alternator had partially seized and, because the alternator belt has to go round the large circumference of the starter ring, it had become an engine brake!
I often simulate this when conducting LPCs and LSTs.