I have had similar frustration attempting to print Amazon Basics black PETG with my built-from-parts i3 clone. I'm using a Bondtech EMG direct drive extruder with an 0.4mm all-metal hotend. I custom built the printer to work with flexible filaments like TPU.

It prints beautifully with ABS, PLA and TPU but I have only succeeded in printing small 10mm calibration cubes with PETG. Everytime I try to print a large item it prints the skirt and brim and jams as soon as it starts printing the first layer infill. I normally use the Prusa version of Slic3r for slicing.

I have tried all kinds of setting experiments:
Cooling fan on or off for the first 3 layers or always off
Hotend temps of 240 to 250C
Bed temps of 80 to 110C
Slowing speeds down from 50 to 15mm/s
Various PETG profiles
Changing the nozzle height above the bed

The PETG filament is more flexible than PLA or ABS but stiffer than TPU. It appears to start out extruding fine and then it comes out too slow for the Slic3r calculations and the extruder coils the filament where it leaves the extruder.

I have no problem with adhesion to my flexible metal bed surface with hairspray. I use a 10mm brim on both PETG and ABS to stop warping.

I have a cellphone holder that I made for my car in PLA. It couldn't take the summer heat so I wanted to print it with PETG but for now I will have to print it with ABS.