In another post here I mentioned fixing Optiquest monitors. The usual issue was you would press the power button and the power LED would flah for a second and... nothing. This is because the output cap of the switching supply would cease to filter the high speed square wave that goes through the transformer. So your DC power supply is now an AC square wave supply. Of course logic circuits don't like that so they will outright fail.
Sometimes there is enough capacitance via decoupling caps, ground planes on the PCB and local filter caps on the logic board so the initial power up works but once the load increases the ripple increases until it becomes AC again and everything goes haywire or shuts down.
If there aren't many, one can just replace all of them.