How many watts should a power bank have?

Which power bank with at least 20,000 is good? Some have 18w and could charge laptops that way, but most of them don't have it included. I'm not familiar with the information. Can someone help me?

"Which powerbank? Some have 18w"

What does this mean? Watt (W for short) is the unit of measurement for power. The power at a given nominal voltage is one of the parameters of power consumers, not power sources.

A performance specification for a battery does not make any sense on its own. The manufacturer would have to provide information about which constellation this performance specification should refer to. The information could possibly also relate to a recommended power limit, to a power at full capacity and a certain voltage drop achieved or the like. More.

I have not yet heard of a relevant normative agreement. That would definitely interest me.

It says: Power Delivery 18W, Trois Sortie (5V / 3A, 9V / 2A, 12V / 1.5A)

It says in English: "Power output 18 W" and in French "Three outputs". The voltage outputs that can be selected with the corresponding current intensities for 15 W, 18 W and 18 W are then in brackets.

From the information "(5V / 3A, 9V / 2A, 12V / 1.5A)" arithmetically 15 W, 18 W and 18 W result. That doesn't get us a step further as long as we don't know what these performance figures should refer to. I have not yet heard of any such agreement. It could perhaps be understood as follows:

"For output with 12 volts, we recommend connecting devices with a maximum of 18 watts (corresponds to 1.5 A current strength) if the voltage drop of x% should not be exceeded." And then a value would have to be entered at x, unless generally agreed. Something could be done with that. After all, the power consumer's output falls well below its nominal output with a significant voltage drop.

Maybe the label is just to confuse customers, it's modern and stimulates business.

Is this one here https://www.amazon.fr/POWERADD-EnergyCell-Batterie-20000mAh-Delivery/dp/B07K2VXH91

Is this better now than this one? https://www.amazon.fr/POWERADD-EnergyCell-Puissante-Recharger-Rapidement/dp/B084WVJVNC

That depends on the respective needs. The first bank costs 2 euro more, offers 20 Ah capacity and 3 output voltages. The second offers 26 Ah capacity, 3 USB outputs and only one output voltage.

What do you need different output voltages for?

For the optional connection of power consumers with different nominal voltages.

For comparison: I also have air pumps for different bicycle valves, lamps for different sockets and laces for different shoes.