Replacement PSU

Where can I source a replacement PSU for an Insiron 3881?

The part number is 3YNRJ and the (slim) supply has two connectors, a 4pin ATX and a 6 pin PCI-e connector, both for the motherboard.  All other power cables, SATA etc. then come from the motherboard.

I have so far only seen third party vendors selling refurbished versions for close to 100 GBP but have had no luck finding a genuine DELL spares sales item.

I have looked for equivalents in vain but none appear to have the 6 pin PCI-e plug - some have an 8 in or a 6+2 but these appear to be designed for GPUs, not motherboards.

It is extremely frustrating to not be able to come to DELL and simply order a simple replacement part, especially since the PC failed only 18 months after purchase and 6 months after the warranty expired!