You can create price alert here, copy coupons and view price history. Let’s see what best price is ATM.
Plug EU, Model M0331C, 0.5A, USB output power 15.5W, Working environment -10°C to 40°C, Length 1.5m, Power cord size 3×1.0mm, USB Input 110-240V~, Material Flame retardant polycarbonate, Weight About 290g, 50/60Hz, Size 62X62×62mm, Color White, Certification FCC CE ROHS, USB Output Single USB output <2.4A, Single Type-C <3A, polypropylene
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($17.99): BGSTHO15
2. ($18.99): 13f142
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 and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGTT10, bGhOnEy10, BGSM15, BGSMOFF, bgshOOp10, BGSAMRTH, BGELIG0920, BgcLuBofErtA10, BG15SH12, BGAFF10OFF
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Do you need price history chart (for all/most countries) for Xiaomi Aigo 15.5W Type-C Charging Cube? 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)).