Aliexpress
Click here… to search for Xiaomi Upgraded Smart Power Plug on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. You can get coupon down below.
Link: Banggood product page
Coupon (27.99 USD): 13f142
(CouponsFromChina.com tip: paste coupon code in your cart and click Apply 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): TTxBG10, 2019SPEDM, BG3CSUM, AFfbG10, BGmienqo, 0e7f33, FBCOUPON1, BGXMI15, BG20CHARGER, BGMBCBLE, BGAFF10OFF, BGCuponation10
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Price history (for all/most countries) for Xiaomi Upgraded Smart Power Plug is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).