USB C Power on XPS 13 9310

@Falconburger  No, that's not correct.  USB-C charging is managed by the industry standard USB PD spec.  The XPS 13 is designed for a 45W power source.  That means that you should be able to use any USB PD power source (wall charger or power bank) that can provide at least that much power.  Support for more power is completely fine.  The system won't use it, but you won't damage anything by connecting it to a 90W charger, for example.  If you connect it to a source that provides less than 45W though, you might see slower battery charging and/or reduced performance, or the system might not try to use it at all.  As for iPad chargers, depending on the model they come with 10-20W chargers, and not all of them support USB PD.  But even for the ones that do, 20W probably isn't enough for the XPS 13 to bother to try to use.  However, I've personally used multiple third-party wall chargers and power banks that support providing 45W or more to charge multiple Dell and non-Dell laptops, including an older XPS 13 9350.  I have wall chargers from Anker, Nekteck, Satechi, and RAVPower, and a USB PD power bank from RAVPower.  They all work very well.

And on the flip side of this equation, Dell's own charger is a 45W charger that supports USB PD, so you would be able to use that to charge other USB-C devices.  I'm not sure what voltages it supports though.  You can check the label to find out.  5V is mandatory, and then it would have to support 15V and/or 20V in order to provide 45W output.  But it may not support bot, and it might not support 9V either.  I'm not sure.  This can matter because some devices will only support fast charging at certain voltage levels, and if your power source doesn't support that level, then the device being charged will fall back to slower charging, even if the power source itself could support the total wattage required.  For example, Dell has a 130W USB-C charger but it only supports 5V and 20V.  So a device like an iPhone that can fast charge at 18W but only supports doing that at 9V wouldn't be able to fast charge from Dell's 130W charger.

In terms of the types of devices the laptop can provide power for, it will probably be limited to either 7.5W or 15W.  On some systems like my Latitude 7480, there's a BIOS option to let you configure the power level the system will support.  I guess if you choose support for higher output and connect a device that requires it, that might result in performance throttling since you're allowing more of the system's power budget to be provided to an external peripheral.  I have a Lenovo ThinkVision M14 portable USB-C display and it works fine with that older XPS 13 9350 I mentioned above, so I would expect it to work fine on your XPS 13 9310.