They knew it existed but they didn't grasp a use for it. If I recall correctly, some cultures made primitive batteries and steam engines and just used them as a party trick/religious focus to zap people or make little toys move.

The real technology booster would be cheap paper and the printing press. Second best would be materials science tech, letting them have processes to make cheap and durable tools and instruments. That stuff took millions of man-hours of trial and error to figure out.