In Genesis 33:20, "El" is the same word as the noun "el", deity or god, here used as a proper name for God. In the Massoretic Hebrew text on which most of the translations are based, there are no upper or lower case letters to indicate when "el" is used in the sense of "a god", or is used in the sense of "God", or as a proper name for God. The reader relies on the context to understand the intended usage, which in this verse is clear. In all cases of "el" or "El", the Hebrew word "el" is pointalized with a tsere diacritic under the first letter, aleph, indicating that the pronunciation in American English terms is more like "Ale" than "El" (as when pronouncing the name of the letter "L").
The word "elohe" is a Hebrew possessive propositional form of "elohim" meaning "god of". So the complete phrase in (my) translation is
El, the god of Israel
Both "elohim" and "elohe" start with the same Hebrew letter as "el", aleph, but the diacritic under the aleph is hataf-segol, indicating that the pronunciation is more like a short "e" as when pronouncing the name of the letter "L" or as a shortened soft "a" as in "Al Capone". So the complete phrase in transliteration is
Ale, alohey Yisro'el
When reading the MT text in Hebrew, there is a noticeable difference between "El" ("Ale") and "elohe" ("alohay"). A reader doing the public reading in a synagogue would be stopped and corrected for not making this distinction, as I was years ago.
Note that the Massoretic text also contains readers marks that indicate the punctuation tradition. In this case there is a tifha under the first letter of "El", indicating that the first letter is accented and that there is a short stop, a comma, after the word. In "elohe" the readers mark is a maaraca at the end of the word indicating that the last letter is accented.
Taken together, the grammar, the diacritics and the readers marks make the distinction between "el" and "elohe" very clear. But confusion between them is natural when reading a simplified English transliteration without knowing Hebrew.
The Christian Standard Bible, Holman Christian Standard Bible and others avoid the confusion to some degree by translating the whole phrase rather than transliterating
God, the God of Israel
and the Good News Translation translates but leaves "El" as a proper name
El, the God of Israel
which, in my opinion, of the popular translations, is the most fair translation to the non-Hebrew reader.
Finally, note that this name for an altar, "El, elohe Israel" is somewhat palindromic as the proper name Israel also contains the proper name "El" at the end. Compare this with the names "El bet El" for God and for an altar respectively in Genesis 31:13 and 35:7.
In the above I have used the names for diacritics and reader's marks and Hebrew pronunciation as used in the Yemenite Jewish community.