Fixed steps versus a dimmer switch
Standard PD offers fixed voltages: 5V, 9V, 15V, 20V. If a phone's battery wants the equivalent of 10.5V at a given moment, it takes 9V or converts down from a higher step inside the phone, generating heat in the handset. PPS replaces the staircase with a ramp: the charger advertises a range such as 3.3-11V or 3.3-21V, and the device requests precise points inside it, re-negotiating as the battery fills. Less conversion in the phone means less phone heat and a faster sustained charge.
Reading a PPS specification
Three numbers matter: the range floor and ceiling (wider is more capable), the current at the top of the range (3A is typical; the flagships here publish PPS to 20V at up to 5A), and whether the range appears on the port you will actually use. On this site PPS ranges are printed in every series table where the model publishes them - for example 65W series models carry 3.3-11V and 3.3-21V ranges, and even the 67W car charger publishes two PPS windows. A charger page that says only “PD fast charge” without a PPS range has told you less than you need for a Samsung- or Pixel-heavy market.
Which devices require it
Samsung's “Super Fast Charging” tiers and Google's recent Pixel charging curves are PPS-based; without PPS they fall back to slower fixed-step charging. iPhones use fixed PD steps and do not need PPS. Laptops negotiate fixed 20V. So PPS is a phone-market specification: essential for premium Android retail, invisible to Apple-only channels. Set it in the purchase order explicitly, alongside the fixed steps - see PD vs QC for the full protocol picture.