Forget that 1st schematic you posted, this is a switch-mode power supply (SMPS). First thing I'd check is the voltage on the primary side buffer capacitor. That greenish round thing on top - probably rated around 2x the AC mains voltage. For example for a 230V input supply, might be rated around 100 uF / 400V.
DC voltage on that should be around 1.4x AC mains voltage, if it's much lower either a fuse is blown, one or more of the 4 diodes (upper left) has failed, or the capacitor itself has died (you'd probably smell that :wink: ). If that capacitor voltage is okay (please post exact reading you get!), chances are either that power transistor, or the circuitry controlling it has failed. Note that diode test or similar on that power transistor isn't reliable as long as it's soldered in - you'd need to get 2 of its wires unsoldered to measure. But first check buffer capacitor voltage?
Btw BE CAREFUL - everything on left side of that 'trench' in the circuit board is connected to AC mains voltage, with power behind it. One mistake here could be deadly! After unplugging, make sure that buffer capacitor is discharged before touching the circuit anywhere. Either re-arrange test circuit / test components without power, or set up measuring circuit & don't touch / move / adjust anything while powered on.
- - - Updated - - -
By the way, product page here: **broken link removed**
No schematic that I can find. Saw a list price of $2.7 somewhere while Googling... :lol: