US Plug.
Go down and check coupons out. Remember to check price history if it is available. What is best price?
Aliexpress
I could not find it on Aliexpress. Click here to search by yourself.
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. Coupons for SONOFF S20 Switch Socket US Plug? Nope, there’re no coupons in Banggood.
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/i1u
Old coupons (from the oldest to the newest): 502C6B, a3af93, e2bcea, elec, SONOFF15, BGBFCR01, 13f142, BG9NY, BGVDay10%off, BGTT10, bGhOnEy10, BGSMOFF, BG15Sonoff
(you can check these old coupons out, but these probably won’t work)
Other warehouses/versions
This item is available in 4 another warehouse/versions!
1. China – SONOFF S20 Switch Socket EU Type F ($-3)
2. China – SONOFF S20 Switch Socket EU Type E ($-3)
3. China – SONOFF S20 Switch Socket UK Plug ($-3)
4. China – SONOFF S20 Switch Socket AU Plug ($-3)
Price history and price alert
Do you need price history chart (for all/most countries) for SONOFF S20 Switch Socket US Plug? There we go. The lowest price was: $8.92.
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)).