5v Power

The 5v power pins are connected directly to the Pi's power input and will capably provide the full supply current of your mains adaptor, minus that used by the Pi itself.

With a decent power supply, such as the official Pi adaptor, you can expect to pull about 1.5A. This varies by Pi model and adapter used. Devices that require a high current - such as LED panels, long LED strips or motors - should use an external power supply.