Most sudden wallwart failures are in the cord or the plug, due to stress.
Avoid "wrapping" the cord around your hand or around something else, instead, "gather" it and secure with a wrap or rubber band.
Avoid stresses to the plug, where the critical molded wire-to-pin connections are.
Good idea to secure the cord *before* the place it plugs into, with at least a light loopknot to something sturdy, rather 5han leaving the plug end subjected to a jerk or pull in the case of someone tripping on the wire, etc. which can cause a disconnect of those critical internal connections.
And sometimes, the things just fail...
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