Both phones have 6” screens with 720 x 1,480px resolution and both are powered by a quad-core processor (1.4GHz, possibly the Exynos 7570 Quad from the Galaxy J4). Both have 3,300mAh batteries and both run Android 8.1 Oreo.
The two phones diverge in terms of memory - the Galaxy J6+ comes with 3/4GB of RAM and 32/64GB of storage. The Galaxy J4+ has 2/3GB of RAM and 16/32GB of storage.
The Samsung Galaxy J6+ has a dual camera on the rear – 13+5MP – and an 8MP selfie camera. In both cases there’s a reasonably bright f/1.9 aperture. The J4+ has a more modest setup with a single 13MP camera on the back and a 5MP selfie cam.
Beyond that, the specs are identical, including the dimensions and weight. The connectivity too, starting with the LTE Cat. 4, to 2.4GHz Wi-Fi, Bluetooth 4.2, positioning (GPS, GLONASS, BeiDou) and optional NFC (region dependent).
The Galaxy J6+ will have a fingerprint reader on the side, whereas for the Galaxy J4+ this is another region dependent feature - only North American units will get it.
So, what are you getting compared to the non-plus models of these phones? Well, bigger screen and bigger battery on both and the dual camera of the J6+. Note that the Galaxy J6 has an octa-core processor, however.
Exynos 7570 has similar performance to Snapdragon 425. The J6+ is likely to be $300+ the same price as Poco F1.
They plan to put dual core but to maintain respect they choose quad core. SpaceX must send Samsung company to moon and never returns.
If they are 2GHz or more its fine! :D