Is there any electrical reason not to parallel connect different brand and/wattage inverter generators? Assuming they use the same cables?

With a question like that, you must have specific equipment you are asking about what you need to make it work.

Just to make sure, are you talking about running(for example) a HF Predator and a Champion invertor together in parallel?

Are they the same wattage? Two 2000 watt units
or
Are each unit different? A 3500w one and a 2000w one

I will admit that I am not the one to answer the question since I have never used a parallel kit on a generator, but I wanted to clarify so that hopefully the question and answer may be more understandable to myself and anyone else that may read this.

I was under the impression that they had to be two of the exact same units and also ones made to run like this... Something in the design and circuitry.

I've seen the same with Car Audio Amps, its called Strapable...
Strap 2 5K amps and get 10K...  Lots of Competition guys do this.

Lots of people parallel completely different inverter brands and sizes.  You are limited to double the capability of the smallest one, UNLESS you unbalance the load as shown in this video.

Just when GD starts to seem unbearable, stuff like this pops up and is why I continue being a member here.

Thanks for the info.

You can also make your own parallel wiring harness.
Parallel generator cords

I've run predator 3500 and WEN 3800 parallel with no issues.

I thought I made that clear - different brands, wattages.

I have a Harbor Freight Predator 3500 and an AiPower SUA2000id and have been running them in parallel for several years.  I converted the Predator to tri fuel with a NashFuel kit a few years back.  The AiPower is dual fuel and has only been run on propane since new about 2 years ago.  I just use the front panel connectors with a 5 foot WEN cable kit from Amazon for $12.  I have run other older gas only inverters with the Predator with no issues.

We had a power outage last week for about 4+ hours and as usual, I got my little cart set up in about 5 minutes and got back to my normal life.  There is no trick or "Gotcha's" for running in parallel.  Connect the cables and the other hookups prior to starting the first unit, then they work normally.

I tap the power output off of the Predator 30A panel plug going into a 3-4 lug adapter.  That feeds a 12 foot 10ga. cable to an outdoor box I wired to my home panel.  I have installed an interlock for the house main breaker, and 2 30A breakers for the panel input.

The gennys seem to balance their output to the load and the larger one takes on approx. 2/3 of the load from what the panel meter displays.  I use a Kill-A-Watt meter to test with monthly, and that seems to be the norm.

This is not rocket surgery by any stretch, and if you do a little research you should be able to confirm and duplicate my results.  I have plenty of pics for those who may be interested.

Generally, if they are inverters they should run in parallel without a problem.  One issue is the Champion panel has square parallel port connections, most others use a standardized round port & cable shield.

I just checked and the AiPower is now on sale at Amazon for $358.54 with free shipping.  2KW, Dual Fuel with a 30 amp panel plug also.

AiPower 2KW Dual Fuel Inverter, $358.54 on Amazon

You can run them. All you gain is double the smallest unit wattage.  The long post above mine shows this is true when he said the small unit constantly takes 2/3 the load.

As I posted earlier, the power delivered between my 3500W & 2000W inverters seems to be approximately the ratio of their continuous ratings (3000W & 1600W).  To summarize, the larger unit = 2/3, smaller one approx. 1/3.