At last a real budget Laptop Power Supply is available for a very affordable $89.95. For those wondering why a converter plug from DC to DC appears to be so expensive, you need to understand that laptops run at around 19 volts. It is true that many motorhomers run direct from 12 volt and yes they do work BUT some models automatically reduce screen output. However the inbuilt battery can NEVER recharge under these circumstances, so there is a slight risk of losing data. What the power supply has to do is boost the 12 volt DC voltage. Depending on your set up though it is far more efficient to do it this way rather than run through an inverter as there are additional loses and of course it costs more initially.

The following comes from the Australian Import Shop and it has the best description of all the Australian suppliers such as Dick Smith and Tandy etc. Everyone seems to have these at the same price!

Laptop Computer Universal Switchmode DC-DC Multi-Voltage Car Power Supply will run your laptop computer from your car battery. This switchmode regulated 13.8VDC input DC- DC converter power supply will increase the voltage the correct amount to run a laptop computer from your car. Input voltage 12 - 15VDC car battery power.

Output voltage features 7 different voltages to suit most laptops 15V, 16V, 18V, 19V and 20VDC @ 3.5A regulated and 22V, 24VDC @ 2.9A regulated. Supplied with 5 changeable output plugs: 2.1 x 5.5mm, 2.5 x 5.5mm, 3.0 x 6.3mm, 1.4 x 6.0mm, 1.7 x 4.75mm. Stabilized output, low ripple and interference
Short circuit and overload protected. High efficiency and low energy consumption. Power LED monitor.

WARNING: Be extremely careful, and triple check that you have the output plug connected with the correct polarity to suit your laptop. Connecting with the polarity the wrong way will damage a laptop computer, If unsure seek professional guidance.

NOTE: As we specialise in buying gadgets like this and then get into trouble, here's our two bobs worth! Make sure that the amperage of your laptop is LESS than the 3.5 amps available from this unit. This is particularly important if you use USB devices powered from the laptop. If you have a laptop with a non-standard 12 volt socket such as the very popular Sony Vaio etc. we suggest you ask the supplier if the adaptor will work with your particular brand.