If that's for an XPS 9305, it should be more than sufficient to power the system (or with the system powered off, charge the battery a few times).  
Will I be able to charge my Dell XPS 1305 with a Anker PowerCore+ 26800 With 60W PD ChargerThe Anker PowerCore has an output of 45W and the battery of my Dell XPS 1305 battery is 5WHr
Advice on what Power bank to buy for Dell XPS 1305