When I look at the vCenter > VM > Manage Snapshots, I see there is on snapshot with "data size" = 3.5 GB. However, when I query using PowerShell, the reported size for the snapshot is almost 0GB. This happens to other VMs as well and PowerShell seems to always returns smaller sizes.
My Powershell just use
get-vm -Name [vm_name] | get-snapshot | select sizeGB
Why the difference?
I suggest you read the post from LucD: