Some users have asked us if you can use a USB Type-C to Type-A cable to charge USB Type-C PC's like the HP Spectre x360 and Dell XPS 13 9350 Laptop using a power bank with a USB Type-A port. To demonstrate that this doesn't work, we use a Nubia PB802 Power Bank.
The Nubia PB802 Power Bank claims to deliver 10.5 watts (5 volts @ 2.1 amps) of charging through each of its two USB Type-A ports.
When the Nubia PB802 Power Bank is plugged into the HP Spectre x360, no USB Power Delivery contract is established given that the USB Type-A connectors generally don't support USB Power Delivery.
Even though 5 volts is offered from the Nubia PB802 Power Bank for 33 seconds, the HP Spectre x360 doesn't pull any current from the power bank.
We can see similar behavior when we use the Nubia PB802 Power Bank to try and charge the Dell XPS 13 9350 Laptop's USB Type-C port. No power contract can be established and no power is pulled.