Windows (and no doubt Linux) automatically manages power to maximize efficiency. This is also true with modern computers, where the processor will automatically adjust its power draw according to the task at hand.
For example, it will consume more power when you're running a resource-intensive task, such as converting media files. In contrast, it will consume less power when you're only surfing the web.
However, you can't manually adjust the power management on a per device basis. There are no scripts or applications that you can use to tell, for example, the optical drive to consume less power, as devices are built and designed a power rating. What you can do is limit the number of peripherals attached to the laptop, e.g. an external storage drive. In addition, setting a profile where the device will automatically shutdown when idle at a certain duration (storage drives have this feature).
I'm not familiar with the implications of having a charger that doesn't meet the power requirements. Maybe someone more experienced here can put a light on this subject. In my opinion, this kind of setup isn't good in the long term.