555 timer problem

I suspect your adapter is unregulated, and the switch just changes transformer taps. The rated voltages only occur if you load the adapter to its full current rating, and even then, there is some tolerance and line voltage effects. If you under load it, relative to its current rating, its output voltage will rise, perhaps rather dramatically. Get a $10 (or less) multimeter from Walmart or Harbor Freight Tools and measure the output voltage under your load.

That's a "Dollar and More" store. No true dollar store sells these and you got a good deal.

See the post from John Popelish. Then add this circuit:

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C1 = .1uF, C2 = 10uF 25V R1 = 240, R2 = 910

Mount the LM317 on a small heat sink.

The circuit regulates the 9V (nominal) coming from your adapter to provide a steady 5.99 volts. The adapter will put out more than 9 volts with no load. You could set the adapter to 12 volts, but that would be of no benefit, and would heat up the LM317 more that it needs to be.

Ed

you did say 110/220 ? i don't know what country your from but are you sure you aren't really using 220 on the input and getting twice of what you think on the output? it seems very strange that a unit like that would be rated to use either voltage with out a line switch option?

sounds like it's unregulated (price would suggest this too)

unregulated supplies give (say) a nominal 6 volts on load, but when not loaded or lightly, the voltage will drift high. I have once such supply that gives 17.5v on no load set to 12v! If this is the case with your wallwart, then you may have been giving your thingy way more that it was expecting (hence the higher volume pumped - the pump was running faster)

Either: A. put a regulator circuit in the output so that 6 volts really is 6 volts. or B. Leave it on 3v if all seems well