Aliexpress
Click here… to search for ROMOSS Sense 6+ 74Wh 20000mAh Power Bank 18W on Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (24.99 USD): BG83a3ba
Coupon (47.25 USD): BANGGOODSD
(CouponsFromChina.com tip: just apply this code in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Old coupons (from the oldest to the newest): BGAFF10OFF, BGCuponation10, 13f142, BGHONEY2110, BG169403, BGHU1006, BGd0346e, BG4caff1
(probably won’t work, but you can try them out)
Price history and price alert
Here is price history (for all/most countries) for ROMOSS Sense 6+ 74Wh 20000mAh Power Bank 18W.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).