You asked for a suggestion, I have one. SMPSUs are not the simplest things for beginners, and this one sounds well knackered. I suggest picking up another piece of e-waste & fixing that. You're not gonna fix them all.

I have to be honest, I have been thinking the same thing, but I was and still am willing to give a go if it is indeed fixable. It's not like the parts cost that much or like I would be risking breaking it, so even if I screw it up completely, then I'm still at the very least learning something along the way.

I do get your point however and I might just throw in the towel if no one can advise as to which "Current Mode PWM Power Switch" I should try (from this link: https://www.mantech.co.za/Stock.aspx?Query=PWM+DIL08and) in order to replace the current "OB2358" part with or if someone can confirm that it's not a part that you could just replace with a similar part from the link.

Anyway, it's neither here nor there. I just thought I'd give it a go and hopefully learn something in the process, which I most definitely have so far..