According to my DB the lowest price is 11.42 USD for Waterproof Car 2 Port (in Banggood). Basically copy coupon, view price history or create e-mail price alert. Do you want to know what the best price is?
Latest coupon and price update (UTC):
Banggood (11.42 USD)
Banggood warehouse is located in China. Is it cheap? Maybe there’re no more promotions for this item, because current price is higher than average (which is equal 10.11 USD) You can get coupon down below.
Link: Banggood product page
Price without coupon: 12.69 USD
Coupon (11.42 USD): BGAMMT03
(CouponsFromChina.com tip: apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGSCM11, BGCAR639
(probably won’t work, but you can try them out)
Aliexpress
Click here… to search for 4.2A Waterproof Car 2 Port Dual USB Charger on Aliexpress
Here are coupons that you can use.
Price history and price alert
Price history (for all/most countries) for 4.2A Waterproof Car 2 Port Dual USB Charger is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).