If u use normal powerbank with no support for power delivery. It's gonna charge the MBP at max 5v 2amps or 3 amps if I'm not wrong. But if u use power delivery compatible. It might use higher voltage .. as today there might be a little to none. But since QUALCOMM quick charge 4 powerbank are coming out. Just wait for it as quick charge 4 supports wide variety of voltages and also support power delivery. So theoretically it will charge MBP with faster speeds