I've got the power

The power supply of my external hard drive just died. Luckily I quickly found a replacement unit in a drawer.

As far as I can tell the drive survived this incident without any physical or filesystem damages. Still this raises some questions:

• Why do I have five unused power supplies in a drawer? I only found two out of five matching devices.
• Why do four out of five unused power supplies have the same connector, but different voltage levels? Isn't that dangerous for the devices?
• How long will the replacement power supply keep up, as it has 20% less power than the previous one?

Maybe you can help to avoid that the last question can be answered to soon. Please contact me if you have a spare 12V, 1.5A, DC power brick. :)