OWC Mercury Helios 3S
Apologies if folks know about this, but it looks like OWC has a new version of the Helios 3 out that looks like it'd be perfect for those who only need a short single or dual-slot 75W card. It ships with a 150W external power supply, and, though it doesn't officially support GPUs, it can supply up to 75W to an attached PCIe card and has a physical x16 slot inside. It also has up to 85W of power delivery, though it looks like that takes a dip if there's a more power-hungry card installed. There could be some firmware limitations we don't know about that keeps it from being useful for an eGPU, but as-is this looks like a big leap forward on the power delivery front from the previous Helios and its AKiTiO counterparts.
I like the OWC Helios vs the Sonnet Echo Express SE I because it's easier to take apart (two thumbscrews instead of 4 normal screws) and it has DisplayPort. This new S3 version has more power (requires 6 pin power connector instead of barrel connector) and is updated to Titan Ridge. Since it uses Titan Ridge, they could have added a USB port or replaced the DisplayPort with a USB-C with DisplayPort alt mode port. I guess DisplayPort is easier to add than USB (less power required).