I used the shampoo in my electric pressure washer recently and it didn't work well.
Keep in mind, I do not have a foam applicator for my pressure washer so I just poured the shampoo (100% shampoo) in the soap dispenser, attached the "soap" nozzle and went to town.
There was no foam, just soapy water. What I expected, but tried just to confirm.
Home Depot sells a foam attachment for around $18. I haven't picked one up but from a previous thread on here, it looks/sounds like it works very well.