Do they need power? I use an hdmi to rca and it's not powered. Edit: it did come with a usb cable to plug into it, but I never needed it. Unfortunately I don't

Do they need power? I use an hdmi to rca and it's not powered. Edit: it did come with a usb cable to plug into it, but I never needed it. Unfortunately I don't know enough about hardware to know what's going on.