Search does not recognize certain punctuation characters, or else treats them as identical to each other (or to a space), so you are correct that searching for PoE+ will return PoE results. This is a limitation of eBay's text matching keyword design.
A quick look through network gear did not turn up an obvious filter option for PoE+, though there may be one in a particular category if you search for it. A filter option would be one way to bypass the keyword limitation.
Try searching for PoE-plus instead to find some possible candidate devices, though you should verify that the models are actually PoE+ versions rather than PoE. Once you have found a suitable model, try searching by model number directly and you may find more results where the sellers have not used a "plus" keyword to make their listings easier to find and differentiate.
https://www.ebay.com/sch/i.html?_from=R40&_nkw=poe-plus&_sacat=0&LH_TitleDesc=0&_oac=1
