I was playing diablo 3 when we had power outage, so it turned off suddenly. When i turned on my ps4 and went back to diablo 3 game all my characters and loots and progress was lost. Can’t find it in ps plus cloud storage or ps system. Need advice please
I’d first back up everything and then refresh the database on the PS4 (it should have gone through its own checksum when turned back on but… I’d do it myself). If you had an external drive connected, make sure it can still be read. It is possible the device itself was damaged and now has unrecoverable/unreadable areas on the data drive in which case, if it was saved to the cloud, you’d want to make sure you can log into that and redownload - if it is not there, and was supposed to be, then you’d contact Sony for further help since its their service that failed.
If you can afford one, I’d suggest getting an UPS (battery backup) so this cannot happen in the future.
However, if your D3 game never got to the point of completing an auto-save, like, completing a bounty, a rift, or something else then the game would not have saved and that is perfectly normal for it to “roll back” to the previous state… which would mean fresh everything, especially if this was a first character on a new account.
Can’t know since you didn’t say or provide much in the way of helpful details.
first time playing d3? Do any of your other games have saves?
I had this happen once to my harry potter games on my ps3, it sucked as i just completed 100% and bamo - lost power and lost my saves for that game. Next day I invested in a usb key and now everything gets back to up the cloud first and if any good progress on any game happens, i exit and write the save to the usb key as well.
Not that helps you right now 
it still amazes me that people don’t bloody well save to USB. It’s there. USE IT. Don’t rely on the internal hard drive of the PS4 to be reliable, nor Sony’s PSN online saving service either.
Another thing - turn off the automatic back up. Back up manually. Be in FULL CONTROL.