Power inverters, transformers, adapters and related equipment.
http://www.tpub.com/content/inverters/
The only drawback with this circuit is that it might latch in the conducting state if the load is too heavy or if there is a short at the output, this requires some kind of protection, on the input line, in the form of a fuse or similar.
http://www.geocities.com/CapeCanaveral/Lab/5185/circuit.html#SC
The 3-terminal push-pull DC-DC converter topology provides isolation for safety, suitable boosting of the fuel cell voltage to 400 volts, reduced cost and reduced size of the energy storage elements in the converter.
http://www.energychallenge.org/2001Reports/tamu.pdf
Most people know that UPSes exist, but many seem to think that there is just one kind of device that goes by that name. In fact, there are several different major designs in use for UPS models.
http://www.pcguide.com/ref/power/ext/ups/types.htm
This circuit inverts the polarity of the input. output is limited to less that 200mA.
http://www.reconnsworld.com/power_voltinvert.html
This simple circuit is a good solution to the powering a dual supply op amp from a single battery problem. The circuit simply takes a positive voltage and inverts it. It uses only one 555 timer and a few other passive components, so it doesn't add much in the way of size and cost to a project.
http://www.aaroncake.net/circuits/vinvertr.htm
simple and inexpensive circuit can produce a dual (positive and negative) voltage from a single supply input, extremely useful for powering opamp and other circuits that require a dual voltage from a single battery
http://www.aaroncake.net/circuits/vinvertr2.htm
This Inverter takes 12 volt d.c and steps it up to 120 volt a.c.
http://www.i4at.org/lib2/inverter.htm
outputs 100 V of the alternating current from the input of 12 V of the direct current.
http://www.hobby-elec.org/e_ckt8.htm