This is a Hobbywing Module-XS Stock Non Polarity Capacitor Module. A capacitor module is for “upgrading” your car ESC. With this capacitor the start-up acceleration of your vehicle will be greatly improved. Besides, the great ripple current endurance significantly reduces the generated interference due to the rapid ON/OFF of the ESC power tube.

For some racers, size and weight is a crucial component of their racing program.  
In that regard there are "smaller" lighter weight Stock style power cap modules that offer an improvement over the standard capacitors, without the added size and weight of the full size modified power cap modules.  These can be used in the popular "stock" or "Spec" class racing.  If size and weight are not a concern, the larger "Modified" power cap modules are the way to go.  If you have size, fit, or weight topics that are of major concern, the "Stock" power cap modules are the way to go.

Features:
Low impedance, low heat generation, great start-up acceleration. The comparison between HOBBYWING capacitor module and other established brand's capapack.
With the great ripple current endurance, the interference generating from turning on/off of your ESC power tube is remarkably reduced.
With the small size and light weight, it’s easy to install.
Specifications:
Size: Standard (1/10th) 
PN86030004
Capacity: 970µf