Power Supply

• Desktop power supplies are capable of delivering hundreds of watts of power output, but typically use around 150w during moderate activity. A laptop computer typically consumes 30 to 40w of power during moderate use and greater amounts of power when the battery is charging. Laptop computers are also capable of performing in a "low-energy" mode, which reduces the amount of power a laptop uses and is designed to preserve battery life.
  
  

Screens

• A laptop's power consumption is used to power the laptop and its LCD screen. Most desktop computers do not have a built-in screen, which means that their LCD or CRT monitor uses its own power supply, increasing the amount of energy being used when the computer is active.
  
  

Processors

• Laptop computers use "mobile" CPUs, special processors designed by the manufacturers to use lower amounts of power than their desktop counterparts. Mobile CPUs need to be energy efficient in order to extend the battery life of a laptop computer; desktop computers have a constant stream of power. The energy efficiency of mobile CPUs means that mobile processors are not as powerful as standard desktop CPUs. Applications that require large amounts of system resources may perform slower on a laptop because of this limitation.
  
  

Components

• Desktop computers are expandable and can hold more components than a laptop computer. High-performance desktops can contain several hard drives and multiple graphics cards, which increases the amount of power they consume. The more components you install inside of a desktop computer, the more power it will consume. Laptop computers contain a fixed number of components and are not as customizable as desktops, but the limited expandability of laptops limits the number of power-consuming components that can be installed.
  
  

Uninterruptible Power Supply (UPS)

• The battery of a laptop computer allows it to run continuously in areas where blackouts and power surges are frequent. Powering a desktop continuously requires the use of an Uninterruptible Power Supply. UPS backups can only power a desktop computer for a short amount of time and consume large amounts of power when charging.