Novak GTB after market power cap
 

Can I solder a cap to the esc as like the tekin esc?
Or do I have to have the original power cap with the board?

Nope you need the proper Novak capacitor, it's got other bits on the little PCB that the ESC needs :)

damit well it works with it solderd there but Ill look at getting a proper one asap

I emailed novak as well as posting here and got a reply that I can just use the cap as its all they use now, the board has been removed.

NICE!!!

Novak Capacitor
 

The Novak Trans cap(acitor) module has a Large Capacitor to smooth out power dips (preventing receiver dropout) and a Hi pass filter to snub voltage spikes.

Depending on your motor/servo/esc setup it may or may not be needed. Finding out the hard way could be a problem.

Won't do any harm to fit one. ;)

Far as i know,the Losi Xcelorin Capacitor is exactly the same,its basically a rebranded GTB.Maybe you can grab one of those more easily.