Yesterday I bought my new powerbank
Powercore metro essential 20000
I had placed it on wall charger (Galaxy S8+wall charger )
Sense about 12 hours till now only 25 % charging diod flashed only ?
Is that normal ?
You should try another charger.
But I remember it can take long to get it fully charged with a normal charger.
The older Samsung wall chargers are adaptive wall chargers which means it can fast charge your phone, but will revert to the lowest power output when charging devices that are not a phone. You need a wall plug that can output power delivery at 18w in order to fast charge this powerbank.
Personally I recommend This wall charger, but there are others you could get to charge this faster.
And even more as Rob mentioned!
If it looks like this:
Then you need to recharge it with a 5V 2A charger. Your charger is going to give 5V 1A as it’s not seeing a Samsung phone it will default to the slowest charging so we’d expect your charger to take 20 hours.
With a 5V 2A recharge is 10.5 hours
If though you got this this which is a Powecore Metro Essential PD (the PD part is important)
Then you need to charge it from a 9V 2A Power Delivery charger.
With a 9V 2A PD then recharge time 6.5h
A good charger to get which will do either is the Nano can do 5V 2A and 9V 2A and you’d need a USB-C to USB-C cable (which you have already if got the 20000 PD)
I can’t tell what country you are in, so I’ll link to a USA and a UK charger to illustrate some chargers to consider.