In some of the model years (2013 comes to mind), there was a *separate* fuse layout manual.
The primary owner's manual did say that the other booklet existed.
(a pause while i download the 2019 Owner's Manual)
Yes, your book says:
"The fuse allocation chart and further information on the electric fuses and relays can be found in the "Fuse allocation chart" supplement."
BUT ... unlike the 2013, MB doesn't have your fuse supplement available on their download site.
(
https://www.mbvans.com/sprinter/owners-resources/owner-manuals )
--dick
p.s. i see that that Manuals site has made a hash of the fuse supplements for previous years.
The "fuse supplement" links for both 2015 and 2013 merely point to the (fuse-less) Owner's manuals.
The 2013 link
used to be valid.