Uuuidgen.exe is a tool from DotNet Framework. You can append "-c" option to generate uppercase letters
Run uuidgen /? to see the detail usage of uuidgen.
Microsoft UUID Generator v1.01 Copyright (c) Microsoft Corporation. All rights reserved.
usage: uuidgen [-xisconvh?]
x – Generate sequential (V1) UUIDs
i – Output UUID in an IDL interface template
s – Output UUID as an initialized C struct
c – Output UUID in upper case
o<filename> – redirect output to a file, specified immediately after o
n<number> – Number of UUIDs to generate, specified immediately after n
v – display version information about uuidgen
h,? – Display command option summary