I have both side by side, and I'm listening to the 2102 as I write this.
Both are KT-88 stereo amps. One is 75 watts per channel 2 X 75; the other 100 with meters.
If you use an original 275 or one of the reissues from the mid 90's they have point to point wiring instead of the new 275 circuit board. Also new ones have slightly different circuitry (zener diodes).
If power and meters are desired the 2102 is the ticket. if you like the retro look and 75 watts will suffice the 275 is a dandy.
Side by side for sound quality with Klipsch Cornwalls I like the 275. With my Magnepan 1.6's I like the 2102.
The 2102 can also do double duty as a room heater or small BBQ.