It never ceases to amaze me what information is online. There's a Wikipedia article on the history of US postal rates [0], which lists several increases in the last few years alone.

It apparently has one small mistake though, because it says the postal regulatory commission (PRC) sets rates, while the PRC website says they only set rate limits and the USPS sets their own rates [1].

[0] https://en.wikipedia.org/wiki/History_of_United_States_posta...

[1] https://prc.gov/who-sets-postal-rates