changing electrical plugs
Don't buy anything mains on eBay

Anything that plugs into mains power should have been certified by a competent testing lab, such as Underwriter's Laboratories (UL), ETL/Intertek, or CSA.  Note that CE is not a testing lab. 

The Chinese make what can best be described as sh** a junkstream of extremely low-quality, dangerous garbage.  They would never waste the testing fee to send it to UL to get listed; they're deliberately breaking every rule in the UL White Book with regards to product safety. In fact, they usually don't fake a UL stamp; they put the CE stamp, which is a meaningless mark intended for products in Europe (where even there it's a voluntary mark; the company swears it self-inspected.) 

This ... junkstream can be seen on full display on a site called alibaba.com, and you see the prices are preposterously low. This is because they are essentially counterfeit items.   They are also sold at retail at AliExpress.com. and also by enterprising marketers (most of them in China) who buy up lots of these items and list them on eBay.   At much, much higher prices. 

They'll buy a $2 knockoff of a $30 item, and list it for $21 because if they listed the item for $5, people would instantly realize it's a fake. 

The markup is so stupid high that they don't care about returns. 

Those marketers also list them on a flea market called Amazon Marketplace, which is sneakily mixed into regular Amazon listings. (under the "Buy" button they say "Sold by XXXXXX" instead of Amazon). Amazon also allows them to dropship into Amazon's warehouse, in which case they say "...and fulfilled by Amazon" and ship with Prime.  Watch out. 

Most countries in the world use 220V.  These cheap factories on Alibaba may not want to make a 120V version of their 220V junk, but if you order in large enough quantity, they'll happily slap a USA 120V plug on it.  And the marketers are too stupid to realize it's not that simple. 

Now granted, eBay and Amazon have everything for sale, and that does include bona-fide parts.  So yes, it's possible to find the real McCoy, but you have to know exactly what you're looking for, and it's the very height of caveat emptor.  Buyer beware! 

The US also has 220V if you need it

If you have a bona-fide 220V item, that's actually doable. The US has plugs and sockets for that, and they're a different shape so you can't accidentally plug one into the other.  You wouldn't do that just to save money on a cheap soldering iron; you'd do that to use a special or exotic piece of equipment, like that perfect coffee machine.