Verses in question:
2 Samuel 23:8: “These be the names of the mighty men whom David had: The Tachmonite that sat in the seat, chief among the captains; the same was Adino the Eznite: he lift up his spear against eight hundred, whom he slew at one time.”
1 Chronicles 11:1: “And this is the number of the mighty men whom David had; Jashobeam, an Hachmonite, the chief of the captains: he lifted up his spear against three hundred slain by him at one time.”
I think there are a few things worth noting here. Firstly, it appears that these two verses are speaking about two different people. For instance, Josheb-Basshebeth, aka Adino, killed 800 men while Jashobeam killed 300. Furthermore, the most literal translation according to the Hebrew text may be the New American Standard Bible, so let’s look there. Here are the verses according to the NASB:
“These are the names of the mighty men whom David had: Josheb-basshebeth a Tahchemonite, chief of the captains, he was called Adino the Eznite, because of eight hundred slain by him at one time.” (NASB 2 Samuel 23:8)
“These constitute the list of the mighty men whom David had: Jashobeam, the son of a Hachmonite, the chief of the thirty; he lifted up his spear against three hundred whom he killed at one time.” (NASB 1 Chronicles 11:11)
This illustrates that two men have different names (Josheb-basshebeth and Jashobeam), different origins, different positions and with different victories (800 and 300). The verses are not talking about the same people, so I don’t think this is a contradiction at all.