I bought a 30000mAh (111Wh) powerbank knowing that it was a fake - impossible given the price, size and weight.
I got 50Wh out of it. It cost €20 which is €0.4/Wh, not bad!
It does PD 5/9/12v 20W and PD charging too. Four outputs.
("99Wh" so that it is airline friendly")