Raspberry Pi 3 B+ install not starting

[c-f-g]

I downloaded the latest image for Raspberry 3 to the very same SD card I used at my raspberry 2 before.
But when I turn it on nothing appears on screen except the yellow lightning flash in the top right corner.
The red LED of my pi blinks 4 times with a long interval, followed by a 4 times shorter interval, holding the red light of the last flash a little longer before it starts with the long interval again.

I tried another SD card, nothing changed.

I tried different other power supplies without changing anything. When I measure the amps it only consumes 0.11 to 0.14A so I think it may be no power supply issue?

[Zing]

@c-f-g For Rpi3+, use The BETA:
https://forum.recalbox.com/topic/16576/february-2019-beta-version