The phrase "enough caffeine" means having a sufficient amount of caffeine, typically referring to the desired or needed level of stimulation or energy it provides. Full definition
I've tried the pumpkin spice latte before, it was fine, but it's not enough caffeine in it for me, haha. (averysweetblog.com)
I haven't had enough caffeine yet this morning. (askmoxie.org)
For the friend or family member who is always on the go (and can never get enough caffeine), this travel mug will surely be their new favourite thing. (styleathome.com)