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Re: No, I want to see how a PSU can be quoted in joules.

Energy in a Capacitor

We know that:

1. Energy = charge × voltage

2. Q = CV.

This second relationship tells us that the charge – voltage graph is a straight line.

The capacitor is charged with charge Q to a voltage V. Suppose we discharged the capacitor by a tiny amount of charge, dQ. The resulting tiny energy loss (dW) can be worked out from the first equation:

dW = V × dQ

If we discharge the capacitor completely, we can see that:

Energy loss = ½ QV

By substitution of Q = CV, we can go on to write:

E = ½ CV2

I'll leave you to do the units ........

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