I was wondering if it was a case of a 6 pin power connector not being plugged in. Some 1650s do have a 6 pin connector. But that one apparently doesn't and should get all its power via the motherboard. So it's not that.
The PCIe slot should be able to power the card. I'd remove the card and check to see whether there is any lettering immediately around the PCIe slot that states a wattage e.g. 35W. Sometimes OEM PCs are limited to less than 75W for the PCIe slot though as far as I know your XPS 8300 isn't one of them,
It's possible the card is DOA. New components arriving faulty isn't entirely uncommon.
It could be worth trying the troubleshooting steps here:
As of lately this issue has been occurring frequently. The fans will spin up as normal but there will be no display, after 10 or so seconds the PC will beep once and repeat it every 10 seconds... I...
www.dell.com
i.e. clearing the CMOS and potentially replacing the CMOS battery. These batteries are cheap and it's usually worth having one on hand if you own a PC, anyway.
It's also possible that even if the motherboard should be able to power the GPU, it can't because it's old and not working properly, I suppose.
There is another possibility, that I certainly wasn't aware of before, which is that the graphics card requires a system with a UEFI BIOS. Which your XPS 8300 doesn't have.
It's apparently a thing, and it might depend on the specific GTX 1650 model.
This EVGA one apparently needs UEFI for instance, or so the people on the EVGA forum say.
The most up to date BIOS officially available for the XPS 8300 is version A06. This is a legacy BIOS and not UEFI - there is no UEFI BIOS for the XPS 8300 it seems. Someone
did manage to cheat and get A07 on it (which is risky anyway), but despite
rumours A07 would introduce UEFI, the person who got it working here
says it didn't. In that topic when some people were having this with much older GPUs, the GPU maker gave them a non-UEFI BIOS for the card, but it's highly unlikely they have these for modern GPUs.
Someone apparently asked Gigabyte if that GTX 1650 OC was compatible with Legacy BIOS but were told
UEFI only. Although customer service reps can say all sorts of things...
This person apparently was told a GTX 1650 Windforce by Gigabyte does work on legacy BIOS. Though I wouldn't necessarily take that to the bank.
(NB: the Windforce, does need a 6 pin connector from the PSU, which you seem to have, and there are plenty of reports of people using their Dell PSUs with new GPUs fine, but at this stage I wouldn't take anything as a given... You can apparently
run a 1650 that has a power connector without it, at least on some systems...)
You could contact Gigabyte support to ask whether the specific GPU you have supports legacy BIOS, and if not whether any of their GTX 1650s do support legacy BIOS.
And return the card as/if necessary, or if you don't hear back from Gigabyte.