Neznajka,
что не так?
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
<script>
$(function() {
var per=1;
$('#infaSpsVal input').eq(per).prop('checked', true)
});
</script>
</head>
<body>
<div id="infaSpsVal" class="marLft borRadBot">
<div class="optWrap">
<input id="rad1" type="radio" name="radTri" value="-1">
<label for="rad1">Papier</label>
<div class="radInd"></div>
<div class="radFon"></div>
</div>
<div class="optWrap">
<input id="rad2" type="radio" name="radTri" value="0" >
<label for="rad2">-?-</label>
<div class="radInd"></div>
<div class="radFon"></div>
</div>
<div class="optWrap">
<input id="rad3" type="radio" name="radTri" value="1">
<label for="rad3">System</label>
<div class="radInd"></div>
<div class="radFon"></div>
</div>
</div>
</body>
</html>