What problems might I encounter buying a DC-AC inverter?

Can the wattage be too high or too low?

The rating can be too low. It’s really not possible to have to high of a power supply since the load only draws a cretin amount.

If so, what will the result be with too high or low wattage?

If you draw 1000W from a 500W supply will burn out the supply or damage the equipment that is trying to get more power than it can. The fuse should trip, but, it could catch fire. So, don’t try and use an inverter at loads higher than what it is rated for.

Are some brands better than others?

Yes, you get what you pay for.

If so, which are the best and worst and why?

Sorry, I’m feeling too lazy to research all the different brands and types, especially since I have no idea what your needs are.

***consider the following

A cheap inverter may be adequate for an RV where you only intend to run a few lights or kitchen appliances but may destroy expensive electronic equipment. The slightly technical reason for this has to do with how “clean” the AC power is. Something like your PC will not appreciated a sloppy sign wave or a bunch of noise on the line so, if you need critical power supplied to expensive TV’s and computers it will be well worth your time and money to buy a higher quality inverter.

Compare the wattage of the AC appliance(s) to be used to the wattage of the inverter.

Compare the output AC voltage of the inverter to the service voltage of the appliance(s).

Compare the DC input rating of the inverter to the voltage of the intended DC power supply.

Compare the wattage or DC amps rating of the power supply connectrion to the rating of the inverter.

How does the inverter connect to the DC power supply ? Where is it located ?

How does /do the AC appliance(s) connect to the inverter ?

Will the power draw of the inverter appreciably weaken the DC power supply ? For instance, will it seriously weaken a car / boat battery over a duration while the engine is off and you cannot restart the engine ?

If the load exceeds the capacity of the inverter, it won't function. On cheap units, reversing the polarity can damage the unit; better units use fuses and alarms.

Yes, some brands are better than others - typically, we're talking about square wave vs. pure sine wave inverters. The kind to buy depends on the AC devices you want to run. For example if you're simply running a light bulb, there's no point in spending the extra money for a pure sine wave inverter, as a square wave will do just fine.