Laptop with 4k Output?

Many models will support this - just about anything with a 7th or 8th generation Intel CPU will - but depending on what you plan to display, you may be less than pleased with the performance.  If 4K video and or gaming is what you're after, the Precision mobile workstations and Alienware models are the place to start.

@ejn63is correct that Intel CPUs have supported it for quite a while, in fact some 4th Gen Core CPUs supported it, but you also need a system that provides the appropriate output.  For example, an Inspiron system with a sufficiently new CPU but only an HDMI 1.4 output will not allow you to use a 4K display at 60 Hz even though the GPU would have supported it if better connectivity had been available.

If you only need a single 4K display at 60 Hz, you need at least one of the following outputs:
- DisplayPort (or Mini-DisplayPort)
- USB-C with video output support
- HDMI 2.0 (most Dell laptops only have HDMI 1.4!)
- An legacy E-Dock connector on the underside of the laptop, plus a newer E-Dock variant that includes USB 3.0 ports (since that also added DisplayPort 1.2 support).

If you need dual 4K at 60 Hz, you need one of the following:
- Thunderbolt 3 (with TB3 dock or TB3 to Dual DisplayPort adapter)
- DisplayPort 1.3 or better (I believe only available on the Precision 7x20 models)

Finally, if you go the USB-C route, in order to get 4K at 60 Hz you will need to use the USB-C port solely for video output.  If you connect a dock or some other breakout adapter thing that has other connectivity on it, such as USB ports, Ethernet, etc., then you will only get 4K at 30 Hz because half of the USB-C port's bandwidth that would otherwise have gone to providing display bandwidth is instead being reserved to support USB traffic.  The exception to this would be if your system supported DisplayPort 1.3 or better out of USB-C, but to my knowledge that hasn't arrived yet because Intel GPUs don't support it yet.