80% efficiency is not unusual. In the past year of monitoring (energy meter @ panel + car readings) I've ranged 51-97% efficiency.
My efficiency will vary based on the ambient temperature at time of charging, the temperature of the battery pack when charging starts and the charge time / amount.
In the dead of winter I have observed 6A @ 240V going into my car for 10 mins with little/nothing going to the battery. The charger allows 40A, but the car only "requests" 6A since the battery is too cold to charge and the power is going to the inductive heater to warm the battery. When this happens I assume that little is going into the battery since the app / car predicts +48 hours to charge, but once the car starts pulling 40A the estimate drops to 1 hour. Obviously for small top ups (<5KWh charge) at cold temps inefficiency will be horrible i.e. 50%.
Likewise in higher temps, power has to be diverted to cool the battery, especially if charging at higher amps. (charge at SuC on hot day and listen to the AC scream!)
I've found that if I'm concerned about home charging efficiency: in winter don't charge if <10KWh will be added, or charge immediately after driving; in summer charge at coolest time of day and not immediately after driving. Spring and fall (live in Canada) are my best efficiencies.
The AC/DC converter also has an efficiency rating which I assume is pretty constant and my guess very efficient. (+98%)
I also observe that my HPWC consumes 0.01KWh / 6 hours (0.04 kWh / day) regardless of whether car is plugged in. I don't bother to include this in my observations unless +4 hour charge.