PCE measures the same broad idea as CPI — the change in prices for goods and services — but calculates it differently. It accounts for how consumers substitute between products as prices shift (buying chicken instead of beef when beef gets expensive, for instance), and it covers a wider range of spending, including costs paid on someone's behalf by employers or government programs.
The Federal Reserve has explicitly named Core PCE (PCE excluding food and energy) as its preferred inflation measure and the basis for its 2% target — not CPI. That's why a PCE release, even though it gets less retail-trader attention than CPI, can move USD meaningfully when it surprises.