Most Fertilisers are constructed to get the NPK ratio , ie Ammonium Phosphate plus Potassium Nitrate gives Nitrogen, Potassium, Phosphorous.
The two forms of Nitrogen ( Ammonium and Nitrate ) will make N higher the P and K ie NPK 15 5 10. The K could be higher by using more Pot Nitrate.
Some fertilisers use Potassium Chloride as the K source, usually budget brands, general purpose or for outdoor " Vegetables and Fruit Trees.
Chloride can be a problem in saline soil or water conditions, and is often already well available to plants.
To compare two fertilisers, try to find out the chemical compound sources for each of the NPK.
Also the exact % of each element. Should be 20% each by the name, 20 20 20 but that isn't always the case.
Sometimes there are quirks in the way the NPK is written or measured.