Somethimes we don't need them.
No because they have different connectors.
well for a flashlight if you dont have batterys
The type of power supply being used (AC or DC) should match the power requirements of the device it will be supplying power to.
computer
it is used to supply power to motherboard and other peripherals
Yes. A Cat-5 line can be used to supply power to certain Ethernet Switches that support POE, or Power Over Ethernet.
Your battery.
The best power supply I've used is the Hurricane digital power supply, it has many features my favorite being that it remembers your last settings.
Variable DC power supplies are commonly used in electronics labs, production lines, and testing environments. They are used to power and test electronic devices such as electrical components, circuits, and sensors. Variable DC power supplies are also used in research and development for prototyping and experimenting with different voltage levels.
No, alternating current (AC) can also be used to charge batteries using a charger that converts AC to DC. The charger will convert the AC power from the outlet to DC power that is suitable for charging the battery.
They supply power to the spacecraft during missions.
Answer for countries in Europe and other world areas running a 50 Hz supply service.AC power supply is 230 v supply used in our homes for switching on fans, bulbs etc. where as DC power supply is used for switching on our laptops, charging our mobiles phones, i pods etc.