As per this Wiki page :
The Super Saiyan transformation comes in response to a need, not a desire.
So does it mean that even if a Saiyan might reach the energy level that a super Saiyan might have, he'll still not get converted to a super Saiyan unless there is a need? Energy level doesn't determine the ability to become a Super Saiyan, but a need to become one does?
On the other hand, as per the discussion on this page, it seems energy level is indeed an important factor.
It's confusing.
It really is confusing, and there is conflict as to what is really happens. I think our best guide is the story itself. For this answer I will be using the anime as a guide. Lastly, please note that this discussion pertains only to Super Saiyan itself, and not Ascended Saiyan, or SS3/4.
Now, Goku himself says, when training Gohan, that it does indeed come from a need, and if needed you can create that need. Though, I'll have to check with the original Japanese, because perhaps this wasn't the best word to use in translation? Considering that he also notes that the pain of loss as an important factor, this leads me to believe that perhaps it is more of an emotional thrust than a direct need per se.
Either way, in my humble opinion you need a mixture of the two (need and power-level.) If I'm not mistaken, no one is shown doing it without both factors.
Goku
Vegeta
Gohan
Now, this is only valid in the act of becoming a Super Saiyan. Later on, once a Saiyan has learned how to control it better, the emotional thrust is lessened (if not removed altogether.) In addition, when higher forms of Super Saiyan are considered, the emotional barrier is lessened even more so, and the emphasis is placed more on power-level, and perhaps skills.
As for other Super Saiyans whose original transformations are not explicitly shown, I leave that up to pure speculation. At least we have three good cases to base our claims on; perhaps the rest just belongs in the imagination.
It basically happens when the Saiyan is strong enough, and there is a surge of strong emotions.
Vegeta achieved because he was frustrated with himself. He had just given up and decided that he would never catch up to Goku. He was also in a life threatening situation. Combine those two and you have SSJ Vegeta.
Goku goes SSJ after Krillin, his most precious friend, is murdered in front of him. Goku's anger explodes and he goes SSJ.
Gohan goes SSJ when training with Goku, but then uses anger to ascend.
Goten goes SSJ when Chi-Chi slaps him. I suppose he was angered and that triggered the transformation.
Both the factors are equally important. Without one the other is incomplete.. A saiyan needs both a great amount of energy and an emotional turmoil as the catalyst.
As per the link
Goku achieves the form out of anger over the murder of his best-friend Krillin
and
Bardock achieves the form out of anger after Chilled attacked a Plant child called Berry,
while Vegeta achieves the form through sheer frustration at his original inability to achieve it, especially over Goku.
While training in the Hyperbolic Time Chamber, Goku tells Gohan that becoming a Super Saiyan is powered by rage and told him to imagine Cell and then Frieza when Gohan said he had never seen Cell, killing all his friends to transform into a Super Saiyan.
This shows that everyone required a catalyst to turn to the super saiyan mode.. It was just made easier that Goku had a high power level which was inherited by both Gohan and Gotan in case of Goku; and Trunks in case of Vegeta.. It is not shown how and when they learnt t transform, so its difficult to define the conditions for the same. But it was easier for them since they possessed a very high level of power.
As further stated on the same page :
The power increases of subsequent Super Saiyan forms are so high that by the Buu Saga, the original transformation has been literally reduced to that of a "child's play thing" (as stated by Vegeta; as both Goten and Trunks can transform and harness the power adeptly at such a young age).
This was mainly done to undermine the first level of Super Saiyan level so that the greater levels could be defined to be more powerful and special in comparison to the first.
The two are intrinsically linked. Every creature supposedly has a threshold that they "can't surpass." Super Saiyan allows the Saiyan to break the threshold completely and become something more than they ever could have been without it. It pretty much only happens when a truly desperate circumstance has forced it out of them, but not just any Saiyan can become a Super Saiyan either.
In the Manga they said, that they need to have a "pure" heart.
At Goku it was pure good and at Vegeta it was pure evil. And than they additionally need a catalyst.
For Goku it was the anger about his killed friends and for Vegeta it was for not becoming a Super Sayan.
In the Manga is not mentioned that they need a minimum or maximum power level.
So I think in normal form they might be much stronger than a Super Sayan and can't transform to super Sayan until they have this pure heart or catalyst.
If you continue reading your wiki source you will notice that there written that there are no more known conditions to become a Super Sayan.
Vegata was ultimately push to the brink and cross over as super being in jeporady of losing his only way off the planet he training on due to asteroids and too many of them getting ready to crush his ship and trap him there and he already been training and exhausted himself when the huge amount of asteriods started coming for him and his ship quickly over whelm off how many their was and exhausted he quickly became in fear of being trap and dying on some worthless planet he quickly try to amp up his energy and fearing he was depleted and needed a energy boost to some up a large amount of energy powerful enough to destroy every asteroid all together instead one by one so his need was met when he needed to boost his enegry the most and excerte extreme amount of power to blow away every asteriod all at once to save himself and ship from being crushed and trap, that's when his need for being super came into effect and quickly boosted him over the brink of exhaustion and gave him the energy to produce attack big and powerful enough to clear every asteroid and save his ship at that point a super saiyan knows what energy level needs to be rechead and what strength is required to cross over and transform super, yes when training you need to acquire that need helps the saiyan push his level above exhaustion that he didn't know he could do that, need keeps the sayian going and powering up instead of stopping and thinking that he can't go no higher with his power level simply trying to power up to cross over will not work a sayian must teach his body in training that super needs to be acquired for the fight he training for in order to win thus everybody reaching insane power levels unknown thinking they are ready for complete cell but cell was designed to be better and the ultimate fighter forced of sayian genetics they did not know and every saiyan studied over the years cell was hatch and created and was a forsure Victor ofform he too just n like frieaze uses the planet to their advantage to distract the sayian from the fight so we never really know if a new born super sayian could beat frieza or cell both killed by their own attacks and downfall the sayians in complete form also explaining his need and the sayain always fight n win attitude is what ultimately gets them to that point saying ultimate desire is to be the best goku just doesn't admit that he too kind but always secretly trains to be the best that and his pure heart and strength and ability to easily acquire techniques destined him to become the dragon ultimately explaining the story line surrounded around goku. , pretty much the same as goku in his first fought with vegeta and his kio-ken times 10! Once a saiyan acquires how to get to super level this ultimately their natural high power level form is mere nothing on the scanners and and just like always they can mask their evergy level at natural form so they basically them become high power sayians in everyday life masking their energy with ease keeping their level right at super and easily transforming to super sayian when they please and then the power up starts just like trunks did vs his fight with cell but did not win after just meshing and harnessing true power trying to use it against perfect cell made of androids and z fighters and ultimately the advantage of super sayians thus doctor was on planet namek and his bug collected cell of super sayian goku,so to answer question simply a need is acquired on training to learn of unreached power levels and keep the sayian powering up with out giving up and needs to learn what that level is the amount of event and rest acquire to reach it, goku says its a need cause it was vs frieza so that's his way of explaining to get to super level, but training and getting stronger and having a sayian knowing that super saying level is real having not seen their own ancestors do it because frezia put the fear in all sayians that they could not reach that sayian level it's a myth so no sayian ever tried to push pass exceretion and train their body to transform, all sayian are super strong and the ability to heal and get stronger after a fight plays a big role shall to a sayian reaching super level, the need is just goku explanation but works as a mind technique to become stronger and better there's always a need a saiyan wants to win their fight thru out the whole dragonball z series so why didn't goku become sayian as a boy faced with some serious needs to win against some tuff oppents? but training and becoming stronger is the ultimate key to becoming sayian so the need plays no part in small trunks and small gotenks being sayian a young boy can not simply reach that power level, so how they do it? Lmao who knows sayian freaks they do what they want and kick ass!!!!! Lol z fighters!
