JSFiddle - React, Tailwind, and code Playground

HTML

<html>
    <head>
    </head>
    <body>
        <form action="" method="post" id="searcher" name="InsertForm" enctype="multipart/form-data">
        
        <input onkeypress="kW2PS();" onblur="kW2PS();" onkeyup="kW2PS();" style="width: 77px" maxlength="3" size="2" type="text" name="powerKW">kW
        
        <input onkeypress="PS2kW();" onblur="PS2kW();" onkeyup="PS2kW();" type="text" name="powerPS" size="2" value="" style="width: 77px">PS
    
        </form>
    </body>
</html>

JavaScript

function kW2PS() {
     out = document.InsertForm.powerKW.value;
     out = Math.round(out * 1.359622);
     document.InsertForm.powerPS.value = out;
}

function PS2kW() {
     out = document.InsertForm.powerPS.value;
     out = Math.round(out / 1.359622);
     document.InsertForm.powerKW.value = out;
}