Next day service was great. Many articles report that HP 800 G2 cannot be upgraded with large ATX power supplies because of the proprietary mother board power connector plugs. The ATX power adapter cables sold on Amazon solve that problem. I'm using a 600 watt ATX, with an RX 590 GPU. The GPU is a squeeze, and the front panel USB plug to the motherboard must be replaced with a right angle plug. But it works.03/01/2024 UPDATE - 1) Purchase the PSU adapter cable with the shorting strap - pins 2 to 1. If you get one without the shorting strap, just short pins 2 to 1. Without the strap the BIOS goes looking for a fan sensor and interrupts the boot up until you press "ENTER"  2) This unit uses the "Secure Start" to ensure no unauthorized CDs can be loaded. If you want to be able to load your own software via CD at boot up, you will have to change the "Secure Start" to "Legacy". Good luck with that! Took me 3 or 4 BIOS changes to make it happen. It's worth it to me!