Just check coupons out (with price alert and history). Let’s see what best price is ATM.
Output: 5V 1 – 2.1A, Capacity (mAh): 5000mAh
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. I don’t think there is an active coupon right now – at least in my database.
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): aff7off, e2bcea, BG3CSUM, bgssaff9, BGaDmITAd, bgchinafest, BGBFAFF2019, BGCITYADS2019, bGpAnDacHeCk, 2020CNY, BGAFF7OFF, bGhOnEy10, BGXMI15, BG15POWERBANK, BGAFF10OFF, BGCuponation10, 13f142, BGHONEY2110
(there’s a little possibility that old coupon will work)
Price history and price alert
Do you need price history chart (for all/most countries) for Xiaomi 5000mAh Power Bank? 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)).