Why do I need a power adapter?
The most common answer to this question is that your power supply on your computer simply doesn't have the correct plug for the item you're trying to power on or it doesn't have enough. Power adapters are usually spec'd out to tell you what each side of the adapter is designed to connect to. For example, if you're dealing with a basic Molex to SATA adapter where you have a 4-pin Molex coming from your PSU and you want to connect it to a SATA powered hard drive, you'd be interested in a female end on the molex side and a male end on the SATA side.
Similarly you can find all types of adapters, splitters, and extensions in our power section related to getting you the right connector at the right length.