I triple-checked it – that’s really $16.99 (coupon included at Banggood). XY-UDP Digital USB DC Converter CC CV 0.6-30V 5V 9V 12V 24V 2A 15W Power Module Desktop Adjustable Regulated Power Supply.
Updated:
Banggood
Warehouse in China.
Link: XY-UDP Digital USB DC Converter
Price: $16.99
Additional Banggood coupons:
1. First page
2. Second page
Aliexpress
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Price history and price alert
Here is price history (for all/most countries) for XY-UDP Digital USB DC Converter. The lowest price was: $9.99.
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)).