Magento 2 Event Observer – Add to Cart After Event

I doubt it's not getting called in config or bundle item. Please try this code in your observer.php.

<?php
class Ucs_CatalogOrder_Model_Observer
{
    public function checkoutCartProductAddAfter($observer) {
    $item = $observer->getEvent()->getQuoteItem();
    if ($item->getParentItem()) {
       $item = $item->getParentItem();
    }
    $walletAmount = Mage::app()->getRequest()->getPost('card_wallet_amount');

    //not sure why calling $item->getOriginalPrice() not getting product's price
    //getting price from catalog model
    $productPrice = Mage::getModel('catalog/product')->load($item->getProductId())->getFinalPrice();

    //adding custom with original price
    $finalPrice = (int)$walletAmount + (int)$productPrice;

    if($finalPrice > 0){
        $item->setCustomPrice($finalPrice);
        $item->setOriginalCustomPrice($finalPrice);
        $item->setCardWalletAmount($finalPrice);
        $item->getProduct()->setIsSuperMode(true);
    }
        //Mage::getSingleton('core/session')->addSuccess($finalPrice); 

}

I ended up using plugin di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Checkout\Model\Cart">
        <plugin name="interceptUpdateProductToCart" type="Mycompany\Inventory\Plugin\Rationingcheck"/>
    </type>
</config>

Rationingcheck.php

<?php
namespace Mycompany\Inventoryrationing\Plugin;
use \Magento\Framework\Message\ManagerInterface ;
use Myvendor\Inventoryrationing\Helper\Rationinglogic;


class Rationingcheck
{
    /**
     * @var Rationinglogic|Data
     */
    protected $_helperData;

    /**
     * @var ManagerInterface
     */
    protected $_messageManager;

    /**
     * @var \Magento\Quote\Model\Quote
     */
    protected $quote;

    /**
     * Plugin constructor.
     *
     * @param \Magento\Checkout\Model\Session $checkoutSession
     */
    public function __construct(
        \Magento\Checkout\Model\Session $checkoutSession,
        Rationinglogic $helperData,
        ManagerInterface $messageManager
    ) {
        $this->quote = $checkoutSession->getQuote();
        $this->_helperData = $helperData;
        $this->_messageManager = $messageManager;
    }

    /**
     * @param \Magento\Checkout\Model\Cart $subject
     * @param $data
     * @return array
     */
    public function beforeupdateItems(\Magento\Checkout\Model\Cart $subject,$data)
    {
        $quote = $subject->getQuote();
        $mappedProductSkus= $this->_helperData->getSku();
        foreach($data as $key=>$value){
            $item = $quote->getItemById($key);
             $productSku= $item->getSku();
              $itemQty= $value['qty'];
                if(Condition ))
                {
                    $data[$itemId]['qty'] = 1;
                    if($item->getQty()>1){
                        $this->_messageManager->addNoticeMessage('Only one item can be bought at a time');
                    }
                }

        }
        return [$data];

    }
}