I would expect that everything you buy from a supplier inside the US to come with a US power cable. If you buy it from China, you're on your own.
Many power inlets have a switch to select between 120 and 240. This is particularly true for ATX power supplies.
Some items don't care which voltage you apply, they'll deal with it.
IEC cables (PC cables) come with a number of male ends depending on country.
I think you're overthinking this. I have been playing with this stuff for 60 years and have never had an issue plugging things in.