TamairTarmac
There are actually 2 ATC Transponders; L & R switched by the crew. The general thrust of his statement is however correct in that most flight critical systems are triplicated and have auto switching.
If it's not triplicated; then in most cases it's duplicated. These systems are never on the same power supply.
As a separate example; a non essential system such as ACARS is a software function within the AIMS system. There are 2 AIMS systems and therefore ACARS; The system uses the VHF system it can tune to, one of three (VHF L, C or R), depending on the aircraft option/vintage it will the go for one of two HF systems (L or R) after that; then on to a single SATCOM connection if enabled and optioned. The pilot can select a source if so desired.
So what he's saying in a nutshell is that something IS fishy leading to the end of this aircraft.