1. I have a USB charger that I got with my first mobile phone in 2004. Will it work with PowerShark? If not, what will?
As much as we appreciate retro-tech, in this case you need something decidedly more contemporary. PowerShark requires any USB-C PD power supply that can output 12V at min. 1.35A (heavily expanded Amigas will need more, see question 7). There is no point in looking for the supply's PD spec version or Profile number, because they do not map 1:1 with voltages actually available. Just check if the required voltage is listed in the datasheet and that's it.

If you are not on a tight budget, just buy a 12V/3A power supply and be done. They are often just a few bucks more.

Also, here is a spreadsheet with more information about USB-C PD power supplies we have tested.

2. But what if I plug a non-compatible charger into a PowerShark? Will there be fire, loud noises, things melting? More importantly, will I damage my PowerShark?
Fortunately none of the above. After power-on, PowerShark's LED will turn on RED, no output will be produced, and that's it. So it makes sense to first try various chargers you have at home, if the LED turns on GREEN, the 12V output is there.
3. What about multi-port chargers?
Many of them perform "power rebalancing" when a new device is being (un)plugged, briefly stopping power delivery to all ports. That obviously won't make your Amiga very happy, because it does not have an internal battery to sustain it throughout these gaps. So either get a single-port power supply, or remember not to play with other ports when you're using your Amiga.

Additionally, keep in mind that many multi-port chargers reduce power available in individual ports, if more than one are in use.

4. How long can I work on a battery?
Forever, if the battery is continuously being replenished. :) Otherwise, it depends on the size of the battery and the configuration of your Amiga. On a machine with no power-hungry expansions you will get nearly 2:30h from a 10,000 mAh battery, or nearly 8h from a 30,000 mAh one. Before getting a USB-C powerbank, do check a) if it provides 12 V, b) how many amps it pushes at this voltage (see question 1 for details). Most of 10,000 mAh powerbanks max out at 1.5A, which won't be sufficient for very expanded configurations (yet still fine for typical ones).
5. PowerShark is so small that I can't bring myself to believe it can deliver enough power for my setup. Can it handle anything more than a barebones Amiga?
Yes it can. The last forty years of semiconductor development did not focus only on CPU speeds and memory sizes. We now have components which can do power conversion with efficiency unimaginable to '80s engineers, and in equally unimaginable form factors. Substantial part of the PowerShark design process was component selection and testing, optimizing for stability, size and efficiency. Don't ask how many prototypes we built on the way.
6. Uh, how many prototypes did you build on the way?
13, starting with this monstrosity:

First prototype

7. My Amiga has every expansion ever manufactured plugged into it. Will it work?
In our experience, people frequently have a somewhat exaggerated idea of their Amiga's power consumption, because most power supplies currently used (including Commodore's and contemporary aftermarket ones) have relatively low efficiency. When the power consumption is then measured at the mains socket, it is often way off from what is really used by the Amiga. Large part of it goes into heating the power supply (and sometimes the cable).

But there are obviously limits. So far we have not seen an Amiga that failed to stably work with a 12V/3A power supply, but it does not mean there isn't a guy somewhere who managed to assemble a configuration that makes lights darken when powered on. Generally though, you should avoid pumping much more power than the Amiga connector - and circuit board's tracks - were designed to carry, and for a very heavily expanded setups, supply power through some additional connection. As we receive more information from our users, we will publish detailed information about the limits and consumption of various setups, but so far our testers exercised configurations with 68030/40/60 accelerators, Vampires, RaspberryPi (3 and 4), ACAs, graphics/networking cards, flicker-fixers, Goteks, external drives, etc., and the largest observed draw from the 12V line was below 2.2A.

8. Does USB-C cable matter?
It does in the sense that some cables are more efficient than others, so if you are aiming for maximum efficiency, you should get a cable with less resistance, especially if your Amiga is very souped up. As is usual, it is difficult to rely on branding and ads, because some claimed to be great - aren't. Here is probably the best site to get more information about specific cables: https://www.allthingsoneplace.com/usb-cables-1 (look for PDF link). Rule of thumb is to get a 5A cable, because it should have a thicker conductor. Out of bazillion cables we used/tested, INIU (6.6ft) 100W PD 5A and uni USB Type C 100W Fast Charging Nylon Braided Cable (5A 20V) worked best, but there are probably equally good ones available in your market (or on your shelf).

BTW, retrousbpower.com is an Amazon Affiliate and may receive commision from products sold through links on this page.

9. How about GaN?
In practice it matters less than the cable, but GaN power supplies are usually somewhat smaller. Go for it if you want the latest and greatest, but you will save more energy by getting a better cable.
10. What protection is present in PowerShark?
There are three types of failures that are guarded against:
  1. Faulty USB-C power supply resulting in under- or overvoltage on 12V input. Unlikely, but since we do not control what power supply is attached, it makes sense to monitor what it delivers. If it goes out of acceptable range, PowerShark stops power delivery and makes its LED red.
  2. Failure of voltage converter circuit inside PowerShark resulting in an overvoltage. Even more unlikely, but since it is well known that impossible things do happen occasionally, and nobody wants to be responsible for frying an Amiga, we check for that and we cut off power if voltage exceeds 6V even for a few microseconds.
  3. Temporary undervoltage caused by PowerShark failing to handle a large load transient. A regular power supply will pretend that nothing happened, while the connected Amiga hangs or does something otherwise undesired. Since the user obviously has no idea what just took place, (s)he may suspect a software problem or be generally confused. PowerShark is not like that - it will enter the lockout mode, stopping all current flow and turning its LED red, so you can immediately see that it was an inadequate power that led to failure.
All this in addition to overvoltage, overcurrent, and undervoltage protection already present in the voltage converter chips.

Finally, PowerShark protects your Amiga by preventing quick powercycles. If either you, an overloaded power supply or some other protection circuit turns off power, the device will only restart after a few seconds - even if the ON/OFF switch is in the ON position. The exact delay depends on the power consumption of your computer, but it will be a few seconds.

11. Can you explain how powershark conserves power and thus extends the existence of life on planet Earth?
Most devices using USB-C power turn on at least partially as soon as the power plug is inserted. They negotiate voltage and current, and then remain on standby, waiting for further user actions. Even if your laptop battery is full and it's hibernated (regular standby needs some power for DRAM refresh and a few other things), the USB-C charger needs to constantly work and provide current.

PowerShark is not like that - when its switch is in the "OFF" position, the device remains totally invisible to the power supply, which believes nothing is connected, and so it remains dormant. Only after PowerShark is turned on, the power supply realizes that the USB-C plug has been inserted, and initiates powering on its voltage converter, starts delivering 5V, and then negotiates the voltage.

12. What's the deal with 12 V being not always available in USB-C power supplies?
It's an exemplary case of "design by committee", where said committee defined in spec v1 what voltages HAVE TO be available in chargers of particular wattage. Later they thought some more, and for v2 they figured it would be a-ok to replace 12V with 15V. After all we're only talking about MANDATORY voltages, and you can keep others, too, so no problem here. There are no hardware changes needed, either. Just add a few lines of code to your chip's firmware and you are done.

Naturally, for manufacturers it was easier/faster/safer/cheaper to just search-and-replace "12" to "15" in their code, rather than implement new features, so this is what happened in at least some cases. Most manufacturers came to their senses very quickly, but there are outliers, too. Chargers that are delivered with laptops or VR headsets usually are missing 12V output. Some (major) brands needed time to realize that getting your chargers blacklisted because of unsuitability for some applications enabled by V1 of the standard is bad for business, etc.

13. I heard somewhere that magnetic connectors for USB-C should be avoided.
We heard that too. Two reasons are usually cited:
  1. Disturbances in the data lines leading to slower data transmission. Very true, but PowerShark only communicates over CC lines, where the PD protocol operates at just 300 kHz, and so is not affected by some minor noise. Worst case, an unreadable packet (wrong CRC) will be retransmitted. Again, speed is not very important here, given how little data is exchanged.
  2. Static electricity. PowerShark has ESD diodes on all lines that lead to the USB-C connector, in addition to ESD protection in the chips that connect there.
But clearly, a magnetic connector is another device in the power chain. This device by itself may be working very well, or not at all. So take a look at its current rating and reviews at the minimum.

And one more thing. Used with a laptop, if you trip over the cable and disconnect it, the laptop will continue working thanks to its battery. In contrast, your Amiga will shut down immediately. While that sounds bad, the alternative is a potential damage to USB-C plugs or sockets or your life and limb, if you manage to trip over in especially spectacular manner.