Is it safe to connect external screen to MacBook via USB-C from the warranty perspective
Why wouldn’t it be safe?
The idea behind standardizing on USB is so that you can plug in 3rd party devices to expand and enhance the functionality of your computer. If plugging in devices voided your warranty, they wouldn’t put the port there and instead we’d still have (our cherished) MagSafe power connectors.
If it wasn’t safe to do something, the manufacturer wouldn’t market that function as a feature of the product.
Since power is supplied to MacBook there is a (small) risk to damage the laptop.
Technically speaking, anything you plug into your laptop has the potential of damaging it.
Since USB 1.0, power has always been supplied – 5V @ 500mA. It is only since the USB Power Delivery Specification was implemented that more power can be delivered; up to 100W or 20V @ 5A.
This is why you should always stick to known brands and avoid the cheap knockoffs1. It’s a timeless adage, you get what you pay for, but still holds true today. That said, it still doesn’t rule out the possibility of a manufacturer defect. While very rare, they do happen; your expensive Dell or LG could potentially damage your MacBook.
Technically we’re plugging in a non-standard power adapter, can it void the warranty?
If you are plugging in a display that provides power and conforms to the USB PD specification, especially if it’s USB-IF certified it’s not “non-standard.” That device is designed to connect, interface with, negotiate, and accept power. You plugging in this device, does not void your warranty.
Do screen manufacturers such as DELL or LG have any agreement with Apple?
Speaking as someone who worked in product management for a hardware manufacturer (in a past life), there are no agreements between companies the spell out any sort of liability assignment or otherwise with respect to each other’s hardware. From a practicality standpoint, this would be absurd – think about how many display vendors there are. That alone would be next to impossible to manage. Now, expand that to all the different USB devices and accessories. There’s no way to manage warranty reciprocity agreements to that scale thus making it totally unfeasible.
From the perspective of the manufacturer, the warranty generally covers the products fitness or in other words, it’s ability to do what it says it will do. If you read the fine print, there will always be a clause exempting coverage for misuse/abuse.
This Warranty does not apply to any non-Apple branded hardware products or any software, even if packaged or sold with Apple hardware. Manufacturers, suppliers, or publishers, other than Apple, may provide their own warranties to you – please contact them for further information 2.
What Voids Your Warranty
In short, misuse, abuse, and anything that’s covered in the warranty language. It comes down to what you can prove.
Software distributed by Apple with or without the Apple brand (including, but not limited to system software) is not covered by this Warranty. Please refer to the licensing agreement accompanying the software for details of your rights with respect to its use. Apple does not warrant that the operation of the Apple Product will be uninterrupted or error-free. Apple is not responsible for damage arising from failure to follow instructions relating to the Apple Product’s use.
1Cheap USB-C Cables Could Kill Your Phone or Laptop; Gizmodo, Feb. 2016.
2Apple One Year Limited Warranty- US ; https://www.apple.com/legal/warranty/products/embedded-mac-warranty-us.html