How can I determine the strength of my own encryption algorithm?
Is there any online community/contest where new algorithms are put to test?

Can someone tell me, if using a custom self-made encryption algorithm (assuming its strong enough) is better that using standard algorithms?
Isn’t standard algorithms better studied by crackers, and thus more vulnerable to crack than self-made algorithms?

Unless you are a crypto-mathematician, I doubt you would be able to come up with a alogrithm stronger than the ones currently available. “Any” algorithm is crackable… “That devised by humans… etc.”… its just a matter of if it is worth while or not.

The fact that “standard algorithms are better studied by crackers” is a testament to those algorithms… in the fact that if they are still under study, they are still secure.

Ditto. The established methods are secure because of their study, not in spite of. This article, while not exactly what you’re talking about, explains in more detail why you shouldn’t do your own cryptography. Look under the “The WRONG Way: Double Hashing & Wacky Hash Functions” heading. Notably, the explanation of Kerckhoff’s Principe, which basically means you need to thrown any concept of “security through obscurity” out the window. These encryption/hashing algorithms work even when the attacker knows exactly how it’s done.