I saw one of the answers that says;
This was actually a huge shock for Palpatine, for even though he'd been told by Dooku that Yoda was actually able to repulse force lighting, something that no light side user was ever known to do, Sidious still didn’t expect Yoda to be able to deflect someone at his level. That is why Palpatine had a shocked look on his face when Yoda began to push back against the lightning.
So that basically answers the question. But here is my question now, Is/Are there any evidence that Dooku/Tyranus told it to his master Sidious? Such as the novelizations,legends and Comics. In other words, I'm just asking if Tyranus telling Sidious that he fought Yoda is justified in the evidences suggested. =)