The full context of the sentence from John Adam's letter to the President of Congress, No. 31, 30 March 1780 may be helpful
It seems that the Presentations of the American Commissioners and Ministers Plenipotentiary have not been inserted in the Gazette, which occasioned some Uneasiness in the Minds of some of our Countrymen, as they thought it a neglect of Us, and a distinction between our Sovereign and others. The inclosed Letters will explain this Matter, and show that no Distinction has been made between Representatives of the United States and those of other Powers.
I ought to confess to Congress that the Delicacies of the Comte de Vergennes about communicating my Powers, are not perfectly consonant to my manner of thinking: and if I had followed my own Judgment, I should have pursued a bolder Plan, by communicating immediately after my Arrival, to Lord George Germain, my full Powers to treat both of Peace and Commerce:
On the page that I linked above, there is the annotation (copyright © The Massachusetts Historical Society):
Although JA here indicates that he would reluctantly defer to Vergennes’ wishes that he not officially disclose his powers to the British ministry, the issue was not settled.
In this context, I would not characterize John Adam's use of "Delicacies" to mean "tact". I think he was annoyed that his power to make peace and trade treaties was not entered officially into the record at the time and that a better interpretation of the word in this context is "squeamishness".
I would rewrite that sentence as
I was not in agreement with Comte de Vergennes' excessively fastidious reluctance to officially announce my powers.
If John Adams had respected Vergennes' tactics he might have phrased it differently. There was some controversy based on how the Gazette of France reported on the US representatives presentations at Court, and it may have been caused or exacerbated by "the Delicacies of the Comte de Vergennes".