Warning: Contains spoilers for Venom: Let There Be Carnage.
After a massive showdown at the end of Venom: Let There Be Carnage, Venom defeats Carnage and eats him - but some viewers have wondered if the consumption will have any impact on Venom's strength. Comic book enthusiasts were clamoring for the on-screen face-off between the symbiotes, and the movie didn't disappoint. Venom is initially apprehensive about taking on Carnage - suggesting that red symbiotes are even more powerful - but is eventually able to bring him down.
Carnage is born from Venom in both the movies and the comics, even referring to him as his father. In the movie, he is transferred to serial killer Cletus Kasady through the symbiotic fusion of Venom in Eddie Brock's blood after Kasady bites Brock's hand. Having ingested the symbiotic offspring, Kasady becomes Carnage's host. The two seem to be well-matched, having a similar thirst for blood and desire to induce chaos, but it is revealed during the fight that the pair does not share the symbiotic bond that Brock and Venom have. It is the weakness of this bond that ultimately allows Venom to overpower Carnage at Venom 2's ending.
While Carnage ended up on the losing side of the fight, his strength was not to be underestimated. He seemed to have the upper hand against Venom for the majority of the fight, due to his shape-shifting abilities that allow him both to swiftly avoid blows and turn pieces of himself into projectile weapons that can separate from the rest of himself. With this considerable strength in mind, it's not a stretch for audiences to wonder if Venom will gain some extra strength by having eaten Carnage. Unfortunately for Venom, it seems decidedly unlikely that he is going to gain any extra powers or strength from feasting on his offspring. The idea that he would become stronger after eating Carnage seems to come from an idea that he would be absorbing Carnage's symbiote powers and properties into himself, therefore becoming stronger. However, unlike the mutant powers of Rogue, Venom is not absorbing Carnage but consuming him.
Even though Carnage is a different color than Venom and has a few abilities that Venom does not, it seems that his additional powers simply come from being separated from the parent symbiote. Carnage was separated from Venom through Brock's blood and took on his differential properties from that, which also explains his red coloring. While Venom seems to be more solid in form when molding around Brock (or the other humans whom he inhabits as host for a time, including Anne Weying, who became the largely wasted She-Venom), Carnage is more liquid in his flexibility because he first took form in blood rather than in a whole human. His power came through his independence from Venom; Venom is not able to take on the same properties as Carnage due to his physical makeup being more complicated.
Because Carnage came from Venom, Venom already possesses Carnage’s power, but cannot display Carnage's singular abilities as a more complicated being. By eating Carnage, Venom is effectively returning his spawn back to his former "unborn" state within Venom's mass, not taking anything he didn’t already have into his cells. Realistically, Venom and Eddie Brock are lucky that Carnage didn't find a host with whom he achieved symbiosis, otherwise Carnage would easily have been able to defeat him at the end of Venom: Let There Be Carnage.