It's not a transformer, it's a step-down circuit. There is one big difference. This charger will not charge my Dell E6400. I tested the output and it was a few tenths of a volt lower, but that's all the mismatch you need for this laptop to reject current. Soldered my old transformer plug cable, has been working for four months and keeps counting. At least they took it back and I got a loan from Revain. But I wasted my time.