Due to the way Amazon commingles their stock at the SKU level, there is simply no way to guarantee that what you're getting is genuine, even if you order "sold and shipped from Amazon".
Even from an authorized retailer - the first thing I do with any flash card is fill it full of a test pattern using f3write, and then validate that it actually reads out fine. Counterfeiting of flash cards is absolutely rampant.
And as a reminder since you mentioned them explicitly, a USB charger counts as 110/220V, not 5V.
I do the exact same smoke-test - as I mentioned I use f3write to fill it full, and the counterpart f3read to read it back and test it.
There's no official Win32 distribution but it compiles and runs without issue on Cygwin. When I get home, I can send you a Dropbox link with a build and enough Cygwin DLLs to make it run in a standard Windows command prompt.
As mentioned on the f3write site - one of the very typical hacks is to make the controller report a larger capacity than it actually has - or a larger capacity than is actually functional/reliable. So this is the obvious test to perform - write it full and see if you can read it out.
Amazon will co-mingle their stock with third parties as long as the stocking unit (typically UPC) matches. So if some retailer sends them fake memory cards you get a fake memory card, "Sold And Shipped By Amazon.com". And of course eBay is full of this junk.
At this point I prefer to buy from camera stores. My theory is that since their customers will be making their livelihood off the memory cards that they have an additional incentive to keep their supply chain clean.
Newegg is probably still OK too, although they are now fronting for third-party retailers I haven't heard of them commingling their stocks yet.