Headphones/splitter issue: Sounds okay in the right ear, but it is extremely low in the left ear

I have some headphones which work just fine on my PlayStation, computer, etc. However, when I plug them into my splitter (and another device was connected), only half of it was working. It sounds okay in the right ear, but it is extremely low in the left ear. The issue probably doesn't come from the splitter because it sounded exactly the same with another splitter. Does anyone have an idea how to fix it ? Ps : I have a Hama audio splitter, and a Hyper X Cloud alpha

Question by KDD on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.