Issues about 'docker export/import' command

when I use the two commands in windows powershell (win10)
docker export [container id] > xx.tar
docker export [container id] xx.tar

the file size of the tar produced by the first command is much bigger than the second one.
Can anybody explain it?

and when I tried the command on the first tar file
cat xx.tar | docker import - image
The computer crashed.

docker import xx.tar image on the second tar file worked well, but on the first tar file it gave wrong message: invalid tar header.


It’s a PowerShell problem:

I recommend just using docker export <cid> -o foo.tar