Oneplus charger doesn't charge the old iPad somehow

I was trying to charge my 2012 iPad using the Oneplus charger but seems like iPad doesn't support it. 

I tried with 2 OnePlus charger and its nada. 

Although randomly it works with the cable. Could be the USB connector issue of the OnePlus charger as when I plug the USB part into other chargers, it starts charging the iPad. 

Interesting case for me.