I said conventional
Although I don't really think any AIP system can be classified as a truly "conventional" mean of propulsion, no more than a backup nuclear reactor.
With France, Russia, China, Germany, Italy and Sweden adopting AIP technology, conventional submarines are a dieing breed. The last truly conventional submarine is probably the German built, Israeli operated, Dolphin class. It's another offspring of the little know TR1700 submarine.
The TR1700 was truly impressive when it was launched in the late '70s. With a huge 6.6MW electric motor and 500t of batteries, it could reach 24kts underwater making it the fastest conventional sub to reach operational status. A few experimental submarines built both by the US and USSR reached even higher speeds but they were experimental and unarmed, mere test beds.