The term supercomputer means a computer which is faster than most normal computers.
So you could say we already have supercomputers on our desks. EINIAC was a supercomputer. And our computers are millions of times faster than it was.
On the other hand, you could say it's impossible to have a supercomputer on every desk... because the minute you have a supercomputer on everyone's desk, the supercomputer becomes commonplace, and ceases to be a supercomputer.
So you could say we already have supercomputers on our desks. EINIAC was a supercomputer. And our computers are millions of times faster than it was.
On the other hand, you could say it's impossible to have a supercomputer on every desk... because the minute you have a supercomputer on everyone's desk, the supercomputer becomes commonplace, and ceases to be a supercomputer.