I have just checked coupons. The lowest price I could get is $11.42 for 4.2A Waterproof Car 2 Port Dual USB Charger (in Banggood). Go down and check coupons out. Remember to check price history if it is available. Best price?
Latest price update (UTC time):
4.2A Waterproof Car 2 Port Dual USB Charger Socket Power Outlet with LED Voltmeter for 12-24V Car Boat Marine ATV Motorcycle – Blue
Banggood ($11.42)
Banggood warehouse is located in China. Is it cheap? From what I can see this price is higher than average price ($10.11). There is one coupon available! Pretty cool, huh?
Link: Banggood product page
Price without coupon: $12.69
1. ($11.42): BGAMMT03
put item in your cart and apply coupon code there after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGSCM11, BGCAR639
(I don’t think these’re gonna work, but you can try ’em out anyway)
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Do you need price history chart (for all/most countries) for 4.2A Waterproof Car 2 Port Dual USB Charger? There we go.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).