Step 1: Diagnosing the Problem
Below is an MS Paint rendition of the first stage of a boot dc-dc. the boost stage amplifies the current from a lower voltage to a higher voltage, all in a DC environment. Read about dc-dc inverters on wikipedia.dc-dc converter (boost)
The boost topology can be made smaller and lighter than huge transformer systems, like an APC or UPS power supply.
At the heart of this system is two N channel MOSFETS. (your inverters configuration could have anywhere from 1 to 4 based upon design)
For those who dont know what a mosfet is, its simple enough to say its a kinda like a really fast switch.
The characteristics of this switch are what determines how much current the dc side of the device can source.
Step 2: Digging Deeper
inside the inverter are the some of the DC-DC converter's main fet's. They are normally clamped to the heatsink.
The first step is to identify them, so grab your spectacle and find a part number. MOSFET'S have many characteristics aside from current and voltage rating. RDS on for example, is the resistance while the fet is enabled. this value should be as low as possible. the higher the RDS on, the more heat is dissapated at the junction, and the more chance for overheating. The gate threshold range is also important. your replacement fet should have about the same range.
Finally, make sure the pinout of your fet is the same and in the same package (EX. mine is a TO-220) dont order the wrong package size! for your replacement fet's
Step 3: Making the Modification
carefully reinstall you new fet's. re-solder back in and reattach to any heatsink.
at this point (when everything is disassembled) its a good idea to give it a trial run.
1. make sure the surface your working on is free of conductive debris.
2. attempt to power up the inverter. (use a current limited source like a power supply/ wall wart if possible, not a car battery)
3. carefully check the output voltage (set meter to vac and check the output side)
4. if the output is 100VAC, try a simple 100W lamp.
5. note, i take no responsibility if you blow up you laptop/ house/ solar-system by following this instructable. prolly not a good idea to plug in an expensive laptop, but a blender / lamp / electric pencil sharpener / your 386 can take a beating and are less finicky to odd power supplies.