Plugged into a 20w circuit - same issue. Tried the test page again and the test page worked. So I...
1. Reset all printer settings.
2. Added new printer
3. Selected "IP" - this brought up the correct driver, which was different from the one the HP install choose.
(The New IP selected driver was "Generic Postscript" - the HP install choose Airprint.)
4. Hit OK.
Is now working like a champ - even on the 15w circuit.
Wow - been looking for that fix for months!