The method: Pink Energon!

There were many forms of Energon. The regular form, the blood of Primus which fueled Cybertronians with life. Dark Energon, the blood of Unicron, who empowers the evil and raises dead Cybertronians. Red Energon, which grants super-speed. Tox-En, Toxic Energon, which poisons all Cybertronian life. But there are likely many other unknown forms of Energon.

Like Pink Energon.

There were many legends about this form of energy. Some said it was the long lost blood of Primus and Unicron's sister, or the wife of one of them. Some said it was created by Primus or Solus Prime or both. Other Primes had been claimed to create it as well, or replicate it. But Solus and Primus were the ones most gave credit for. The truth was hidden in the past, unknown by all but the most ancient.

Whatever the case, the Energon was known for two things. It acted like regular Energon, but much more powerful then the regular kind. However, it had a secondary effect. It caused the Transformer or similar life form taking it to morph into a Femme, a female Transformer. Femmes looking to engage in reproduction of their species.

So when the unknowing Decepticons discover this type of Energon and use it... A lot of Transformers are in for a surprise.