In this answer, coin selection was discussed both pre and post RingCT.
Once Ring CT is merged, each transaction will typically have two outputs, growing the TXO set by the same amount
What is the reason why two outputs will be most common? In what situation would the number of RingCT outputs be higher or lower than two and why?
The most common scenario is for a transaction to have an output going to the destination, and an output for change going back to the sender. Since the amounts are masked, there is no need to split them into several outputs by denominations as Cryptonote does.
If sending to multiple addresses at once, a transaction will have more than two outputs.
If there is no change, a dummy zero amount change is generated and sent to a random address, so a one output transaction is not possible right now (but the consensus will allow it).
