I have the same issue.
I got 3x Dell P2213 monitors all connected with displayport to my Sapphire RX480 8GB. Using drivers from the AMD website will make all monitors loop to and from "power saving mode". The only way for me to get it to work was to download the old driver Sapphire has on it's website. If I try to upgrade or install any drivers from the AMD website I will get the issue.
Running Windows 10 1607, tried completely reinstall the computer but I continue to get the same issue.
Someone posted on the Dell website aswell P2213 in infinite "power-saving" loop with display port on rx 480 - Monitors Forum - Peripherals - Dell Community Tried the steps from the Dell support, still the same results.