It is voltage. The LM2596 step down converters I use to power the 12v noctua extruder fans have a display with a pot for adjustment and a button to toggle between input or output voltage on the display. In the picture it is showing input voltage which is the 24v power supply output at 23.9v. Here is a link to the step down converters I use: https://www.ebay.com/itm/DC-DC-Buck-...wAAOSwY45UMfSP