° Power is almost always stored on DC batteries.

° Converting (DC to AC, or/and AC to DC) makes you lose about 20-30% of your capacity

= Use as much DC as possible!

if you want to charge a phone from a power station. Use the USB or DC ports that is has. This can save you 20%+20% (battery DC to AC and back to phones DC)

Don't charge a power bank, to charge a phone. Every converting step takes a bite out of your capacity

But basically all big or motor/compressor appliances run on AC and changing them to DC requires skill and time and money. Although doable for me, I would not recommend this to anyone without them having an Electrical Engineering degree

Almost everything is powered by AC. The things that actually work on DC like electronics, have power adapters to convert AC into DC for the device, like the little brick that comes with your laptop or phone charger.

There are rare exceptions, but EILI5 doesn't care about those.

If you have examples, we could clarify.

I have never seen a consumer product that has a 2 or 3 prong plug that expects DC on that plug.

aka

Anything with a 2 or 3 prong plug, as in, anything that plugs into your wall of your house, that will want AC. If the device is powered by like, a USB cable, that’s going to be DC.

Based on the fact that you're asking this question, it's safe to assume pretty much everything you use is AC powered.

The "charger bricks" for some of your electronics convert AC to DC for you, but trying to bypass them "for efficiency" has a high probability of ending poorly.

Get/use AC on your backup system

if you're running off a battery bank, then run as much DC as you can. if a generator, AC.

Changing power types is inefficient.

Batteries (which is what your emergency power supply uses) and solar panels are DC. They will be most efficient powering other DC devices directly.

Rotating generators (powered by engines, turbines, wind, anything that creates movement through motion pretty much) are AC. They will be most efficient at powering AC devices directly.

As soon as you're changing DC into AC, or AC into DC, you're losing power (usually a quite significant amount) in the conversion process. DC->AC requires an inverter. AC->DC requires a rectifier. Both are inefficient.

The direct answer to your question is that your DC power bank will be most efficient powering DC devices, and less efficient powering AC devices.

It's going to depend on each individual's power requirements. Some things use straight AC power (lamps, refrigerators), others DC (computers, most electronics, bare batteries). Those examples are not definitive. You need to check every item you want to put power to and go from there.

For most people the short answer is, mains power is so reliable that it's not worth your bother to worry about the emergency situations. As long as things work, even a significant amount of inefficiency doesn't add up. So stop worrying, just get things working.

If, on the off chance, you actually are using emergency power a lot, for whatever reason, then yes, this is a worrying about. In that case, you no longer want a short answer. You need a long, complex answer that covers all the different possibilities. So you need to start studying. Be prepared to spend months working at all the details for your specific situation.