As per the Cambridge Dictionary, 'whence' is a more curt form of 'from where'.
Yet, the very first usage examples reads:
It has been returned to the shop from whence it came.
(emphasis mine)
Indeed, looking at this older question, it is sometimes acceptable to combine 'whence' with an additional 'from'. (Pretty sure I have seen this usage in a different Shakespeare text than the one cited, so I have no reason to doubt this.)
The big question is now of course: when?
That is, are there
- cases where using an additional 'from' would definitely be out of place
- cases where using an additional 'from' is definitely "better"
?
(Presumably there must be a wide array of cases where it does not matter either way - no need to specifically mention these, unless of course those were all the cases, without exception.)