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I'm having problem getting any output from this universal adapter for my older laptop, so I opened it up to see this rubber-like white substance inside, on top of the big 68uF 400V capacitor.Laptop DC adapter

A closeup: closeup

If it is glue, why would they use it? It fits well without it, with the leads of that capacitor bent as they are.

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    \$\begingroup\$ You gotta love all the safety and protection components that clearly could be installed on that board, but have been replaced with wire jumpers or left out entirely. Aaaahhh, quality Chinese products! \$\endgroup\$ Jul 11, 2013 at 4:20
  • \$\begingroup\$ I like to think that there is actually only one, giant circuit board design in China that they break off and use for every electronic component in the world. \$\endgroup\$
    – scld
    Jul 11, 2013 at 12:15
  • \$\begingroup\$ Another application is for magnetics to stop vibrating. A common thing is after years they dry out and you hear them making annoying sounds. \$\endgroup\$
    – PlasmaHH
    Apr 1, 2015 at 9:38

2 Answers 2

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A lot of times you'll use glue/epoxy to protect against a mechanical shock (i.e. dropping it). Put it on the at-risk items, like the biggest capacitor, and you have more anchor points with less stress on the solder joints.

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Generally this is a silicone elastomer which as mentioned helps to keep large components in place or closely spaced components from touching.

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