Power supply hissing noise

I have a thunder t350 that gives my charger low voltage errors even though it shows 14v. I was wondering what could cause the hissing and if it could be easily repaired.

I left the charger plugged into the power supply not charging anything and the PS was on, hot and was making a hissing, crackling noise and the fan was also on. The charger was hot and the fan was going low, high,low as well as the hiss/crackle

That's not a good noise for a power supply. You should pull it apart and see if a capacitor has failed and is boiling or something.