If you're trying to sing high notes by pushing, yelling, belting and strangling - then you're never going to sing high notes easily.
The key to singing high notes easily is obviously to get a solid foundation for your voice first; you know, all the standard stuff people talk about like breathing, connecting head and chest, placement - all the basics that are imperative to learn if you want to become a better singer.
But that's not what you're here to learn, right? You want to sing HIGH notes and go crazy in your high range like Chris Cornell, right?
The key here is actually to understand and utilise your vowels.
Yes, your VOWELS are key to singing higher notes with ease.
Let me explain - so, the 'pitch' that you're singing is a result of your vocal folds vibrating, the frequency or 'speed' of which dictating what note you're actually singing.
Now, your VOWEL, is also a frequency (two, to be exact) - and like your pitch, it's also derived from vibration of the vocal folds. However, the vowel you sing is really how you receive the different length(s) of the accompanying soundwaves external to your pitch.
Let me keep this simple for you and rephrase - your vocal folds vibrate, creating a frequency which rings as your pitch, but a derivative of which ALSO rings out as your vowel.
So, you can see where the conflict of interest happens in this equation - your pitch is a frequency that comes from vibration of the vocal folds, and your vowel is a frequency that comes from vibration of the vocal folds.
If you increase the speed at which your vocal folds vibrate, what then happens to the frequency without your vowel?
This, my dear Mr. Watson, is why you've been unable to sing high notes - even after spending weeks/months/years on the YouTube loop of video after video practicing weird monkey sounds and 'mamama' exercises over and over again.
You're literally asking for the same color of vowel in your lower range to your higher range, and there's a disconnect in the frequencies.
You've probably experienced this before - when you go for a high note, you either put importance of the note itself over the word, and you can probably hit the note okay, but the word sounds WEIRD, right? Or, you might be putting precedence of the word and vowel over the pitch, meaning the word comes out okay - but you have to push, shout or flip to hit that same pitch.
Here lies the secret to all high, powerful rock singing - as you ascend, you need to receive the frequency of the vowel differently to your lower range. You can try this now - sing "hey" as a sustained sound. Now, slide up higher in your range and see what happens to this sound.
You start to push, or it flips, right?
Now, try it again, but instead of holding onto the word "hey" - let's move it towards an EH sound more like the word head - so, "hey" to "head" in the back of the head as you sing higher.
The vowel shifts with the pitch, right?
Congratulations, you just discovered vowel modification - literally receiving the frequency of the vowel in a different/more appropriate way as you ascend in range through different registers.
Here's an easy way to discover your higher range;