Power & Source of Big Ideas

I have ordered a new R5S from amazon, but the results are 100% the same. I flash the SD to eMMC image, all goes well I reboot the R5S without SD card and wait for let's say 10 minutes The only cable connected is a cable to WAN (it's from my switch) I browse to the assigned IP address and I get "...
On my R5S I have tried FriendlyElec, 21.02 and 22.03 from the official downloads. I have used the SD to eMMC install and everything seems to be ok. Then I reboot and I'm able to log in and do whatever I like, but after a few minutes I get connection refused. If I reboot I can use it again for like a...