[NAME]  XPS 15 9500 systems that do NOT have an NVIDIA GPU are only designed for 90W, so if you have an Intel-only configuration, you would be fine.  But otherwise, if your system is designed for 130W, then no you're not going to be able to run it at full performance from a 90W source -- otherwise Dell wouldn't have needed to design the system for 130W.  The symptoms you're most likely to encounter are slower battery charging and throttled CPU and GPU.  The system would be unlikely to drain its battery while connected to that source, because most systems will throttle performance in that situation in order to operate "sustainably" rather than operate in a way that would cause them to potentially die even while connected to power.  That said, there are some other systems -- like the XPS 17 9700 and certain gaming systems -- that use "Dell Hybrid Power", where the system actually IS designed to potentially drain the battery even while on AC power during heavy load periods.  I think that's a lame design and that Dell should have simply shipped the system with the power source it requires rather than using an undersized power source and using the battery to pick up the slack when needed.  That imposes needless wear on the battery, and if you have a long-running intensive task, then your system will eventually throttle if you drain your battery low enough, AND you might end up with practically no remaining battery life whenever you do finally disconnect from the power source.Anyway, in terms of a solution, the only options are either Dell's 130W power source or one of Dell's docks that are rated for providing 130W over USB-C/TB3.  Since you're dealing with an XPS 15 9500 and also a 4K 60 Hz display, the only dock that would provide 130W and allow 4K 60 Hz output from that system is the Dell WD19TB.  The regular WD19 can also provide 130W if you order the version that comes with a 180W power source (rather than the 130W version that only passes through 90W), but it can only support a single 4K 60 Hz display when connected to a system that supports DisplayPort 1.4/HBR3 over USB-C, and the XPS 15 9500 only supports DP 1.2/HBR2.  (The specs page that as of this writing claims DP 1.4 support is available from the non-Thunderbolt port on the right of the system is incorrect.)  By comparison, since the WD19TB uses Thunderbolt 3 rather than USB-C, it would allow you to run dual 4K 60 Hz displays if you wanted.  But as of this writing, Dell doesn't have any USB-C displays that provide up to 130W.  And since 130W is above the 100W max of the official USB Power Delivery spec, you're not likely to find 130W support on any non-Dell products at all.  Dell did something proprietary on some of their systems, docks, and power adapters to support 130W over USB-C/TB3.
Hi, I think I might know the answer to this question, but I would like to confirm.  I'm set to purchase the U4320Q monitor that includes USB C input; however, part of my intention is to use a single USB C cable to deliver video and receive power to the laptop. I read in the tech specs that the monitor only delivers 90 watts of power and ofcourse the full power of the XPS requires 130 watts.  Will the laptop be able to run with full performance in this configuration (and maintain enough power to make it through a day of work?) Is an alternative available outside of using the power adapter that came with the laptop?
XPS 15 9500 and U4320Q monitor - USB C Power Delivery