What did Yisro mean when he said that Hashem is greater than all the other gods? Did he know them all?
Rashi: Yes, he did! There was not an Avodah-Zarah that he did not try out.
Why did he say "Atah" (in the present) and "Yada'ti" (in the past).
Rashi: He meant that although he had already discovered that Hashem was greater than all the other gods, now he was convinced.
Toras Avigdor: He already knew Hashem
What did he mean when he said "Ki ba'Davar Asher Zadu aleihem"?
Rashi, Seforno, Targum Onkelos and Targum Yonasan: He meant that Hashem paid them back in the same way as they had dealt wickedly (Asher Zadu) 1 with Yisrael (Midah Keneged Midah) in that He drowned them in the sea, 2 just as they had drowned the Jewish babies, 3 something that no other god was capable of doing 4 .
Ramban: Because he perceived how, in spite of the decree "va'Avadum ve'Inu osam ... ", Hashem punished the Egyptians because they did what they did (not in order to carry out the decree, but) out of wickedness. 5
Rashbam: Because Hashem exacted punishment from them for each and every harmful act that they perpetrated against Yisrael 6 ; whereas all other gods are incapable of avenging the Tzaros of their adherents.
In fact, on a play of words, translating "Zadu" as boiled (as in the Pasuk "Vayazid Ya'akov Nazid" [Bereishis 25:29]), the Gemara in Sotah (11a) explains "Hashem boiled them in the pot in which they boiled (Yisrael [Rashi]).
And that He killed their firstborn, just as they had killed the babies of Yisrael, whom Hashem dubbed His firstborn (See Shemos, 4:22, 23 [Seforno]).
Which He achieved by manipulating their hearts after they refused to obey Him (Seforno).
Whom even their adherents believed were restricted to one type of punishment [Seforno]).
Perhaps this is why Hashem brought 900 million angels (Midrash Sechel Tov 12:12) against Egypt at Yam Suf, i.e. a separate angel punished each Egyptian for each Yisrael that he afflicted. (PF)