I have an inexpensive 12vdc to 120 vac power inverter (300 watt). I use
it in my car for powering my laptop computer and use it when I am
camping for running a small fan, and more.....

It used to work fine, but for some weird reason it seems slow to startup
these days. It has a green light (ON) and a red light which indicates
it's not ready to use. That red light used to just come on for a second
when I turned it on, now it takes up to a minute.

Even more weird, I plugged it into a portable 12v battery that needed to
be charged, and the inverter would not start (that's normal). But when I
plugged it into my car (with fully charged battery), it still would not
power up. I had to turn it on and off several times. Finally it kicked
in. (As if it memorized that weak battery).

Obviously the semiconductors in the inverter still work, or the inverter
would not work at all. I know there is not much else in these things,
but I believe there is a capacitor. (I have not opened it yet). I'm
wondering if the capacitor is getting weak?

I'm not gonna stick a lot of time or money into this thing, but if it
just needs a cap, I'll fix it..... Othersise I'll just buy a new
inverter.

Any inverter experts out there?