Samsung
Free PNG images in the category “Samsung”: 7 files with transparent background, no sign-up.
Screens rather than logos: a flat-frame television hung on a wall with a black-and-white zebra photo on it, and a slim monitor on a flat stand showing a blue abstract wallpaper.
Filters
Samsung The Frame TV 4K resolution PNG
LED-backlit LCD Computer Monitors Samsung PNG
Samsung Galaxy J7 Pro Samsung Galaxy J5 PNG
Samsung Galaxy S8+ Telephone Android PNG
Samsung Galaxy S8+ Samsung Galaxy S Plus PNG
Samsung Galaxy S7 LTE iPhone Android PNG
Samsung Galaxy S8 Samsung Galaxy J7 Screen PNG
In the brand section
This category sits among Logos and Brands, but its images are devices without visible marks. They show the kind of electronics people search for under the name — televisions, monitors, phones — rather than any official artwork.
Using device pictures
A product shot does not make you a partner of the maker. Keep devices generic in ads and avoid implying endorsement; for official logos, the brand's own press kit is the right source.
Swapping the screen
TVs and monitors seen almost head-on are the easiest to mock up: drop your picture into the screen area and keep the frame. Match the aspect ratio, or the new content will look squeezed.