Charging via USB-C power supply (Power Delivery DC-In) - TUXEDO Computers

Charging a notebook via USB-C (Power Delivery DC-In)

We often receive questions about the possibility of charging our notebooks with a USB-C power supply or USB-C docking station as an alternative to the original power brick. The reason is obvious: It is much more handy to charge all devices like your smartphone, tablet and your TUXEDO notebook with a single universal power supply.

In the following, we describe the basic differences between original power supplies for our Linux notebooks and USB-C chargers and why these do not enable full performance for technical reasons.

What distinguishes a USB-C power supply from the original notebook power supply?

At first glance, you might think: Only the port through which the Linux laptop is supplied with power from the charger. But unfortunately, there is much more to it.

To begin with: Most of our notebook power supplies use the common barrel plug that follows the industry standard IEC 60130-10 with an outer diameter of 5.5 mm and an inner diameter of 2.5 mm. This means that you can not only find a variety of power supply units compatible with your TUXEDO notebook in different sizes and power ratings as travel or spare power supply in our online shop, but there is also a chance that you can reuse the power supply unit from your old TUXEDO notebook.

Notebook power supplies are responsible to reliably supply a laptop with enough energy at any time and load condition. However, the rated power of a power supply unit is by far not sufficient to absorb so-called load peaks, i.e. conditions in which individual components draw much more power for fractions of a second. It is precisely for these conditions that conventional power bricks include a high power reserve (“surge power” for 96 milliseconds). If these power reserves are not available, the power supply unit can overload and switch itself off (overcurrent protection, OCP for short) or even be damaged.

This is where the serious difference occurs: USB-C chargers have much lower surge power reserves for several reasons. They are primarily designed for much less power-hungry devices, such as smartphones, tablets or power-saving notebooks, and even with these, USB-C power bricks are primarily intended to charge their batteries in a switched off or a low-load state. Last but not least, the implementation of higher surge power limits would make USB-C chargers more expensive and bigger. 

Throttling performance to ensure sufficient power supply

USB-C power supplies therefore usually have much lower power reserves for peak loads, which cannot guarantee a full power supply at all times.

Manufacturers circumvent this problem by intentionally slowing down individual components, e.g. the graphics card, in order to avoid load peaks at these components and to retain sufficient capacity reserves for the rest of the system.

The dedicated graphics card “gets the short end of the stick” because - in contrast to the CPU - it is not needed for the basic operation of the computer. If the CPU, as central processing component, were to have its performance throttled, the entire system would slow down massively. For those technical reasons, it is desirable and essential for safe operation to throttle performance on “unnecessary” consumers or even to limit the CPU’s performance in order to ensure a sufficient power supply at all times.

In addition, it is important to consider the primary purpose of the USB-C charger: If the battery is fully charged, the power brick only has to ensure the ongoing power supply of the system. However, if the battery needs to be charged in parallel, the USB-C power supply must divide its capacity, which means less power (=performance) is available for the CPU. You can set the prioritisation in the TUXEDO Control Center: Priorize battery charging speed prioritizes charging speed of the battery and provides less power to the CPU. The option Priorize performance prioritizes CPU performance at the expense of slower battery charging.

What requirements must a USB-C power supply meet?

USB-C power supplies are of course always suitable for charging the battery with the laptop being switched off or running under low load. The basic requirement for the ability to charge a notebook via USB-C is a voltage of 20 volts. Many smartphone chargers have a voltage of only 5 volts and do not provide enough power for charging a laptop.

The rated power for a power-saving operation should be at least 65 watts, which requires a current of 3.25 amps (20 V * 3.25 A = 65 watts). For higher performance at least the same nominal power as the original power supply is required.

Due to the current limitation of the Power Delivery DC-In standard to 100 watts (Extended Power Range, EPR for short, with up to 240 watts is still hardly widespread), full laptop performance cannot always be accessed as described above.

The operation via USB-C charger is only recommended with deactivated NVIDIA graphics. This can be easily done via the TUXEDO Control Center (click on the taskbar icon » Graphics » Select built-in) or via the UEFI/BIOS firmware.