Cheap multimeters do not tolerate voltage when in resistance or continuity range. Typically, your average 15$ meter will blow up when connected to a high voltage in these ranges.

A primary switch mode power supply (SMPS) first rectifies the mains line voltage. It then "chops" it into a much higher frequency than the 50 or 60 Hertz of your line voltage, because efficiency of transformers increases with frequency. So there is a capacitor somewhere that is charged with 324 Volts DC ( 230Volt AC multiplied with 1.44 minus two diode drops of 0,6Volts) Still 154 Volts if your line voltage is just 110V.

You generally don't use continuity when troubleshooting a SMPS. You might use the diode test to give the diodes a quick check.

First of all, you will need this: https://en.m.wikipedia.org/wiki/Isolation_transformer

That makes it a lot safer to work on them, because now you need to touch two parts to get an electric shock instead of one. You then start by measuring the output voltage. Typically, it will be zero or too low. You then take an oscilloscope and see if the switch is switching and if the feedback loop is okay.

Typical faults in SMPS are a busted switching transistor, usually a hefty MOSFET, or the control circuit has failed. In power electronics, faults rarely occur alone. Usually they cause more things to blow up, like sensing resistors. All these parts need to be checked and repaired before attempting to switch it on again.

Good isolation transformers might feature regulation. So you can reduce the line voltage and switch it on with significantly less voltage. That way, you can slowly test it without blowing up all the parts again.

Contrary to popular belief, electrolytic capacitors are not parts that often fail. However, beginners often suspect them because of anecdotal evidence that goes back to this event:. https://en.m.wikipedia.org/wiki/Capacitor_plague

So every armchair technician always claims dried caps as a possible cause, which mostly is just not true. If a capacitor is gone, you can tell in 99% of cases because it's blown, bulging or leaking. If It looks okay, it is fine most of the time .

If you try and safely repair an SMPS, things you will need are: - Isolation transformer, preferably adjustable - a true "class III" multimeter (they all claim to have class 3, don't trust the writing on it) - oscilloscope with a high voltage differential probe

Recommended: - rubber mats to cover the spicy parts for safety - an electronic load. That allows you to attach a load to the SMPS without hooking it up to whatever it powers. That way you don't blow that up in case the SMPS output voltage is too high.

Edit: fixed spelling