HP advise against graphics and PSU upgrade

As long as you don't damage your components installing the parts, your fine.
Just make sure you get an HP compatible PSU (they tend to use different connectors). Then upgrade your video card and your done.

However, if you have a scoop over your video card to direct airflow, you'll want to make sure everything fits  .

What HP desktop computer uses "different connectors" on their PSU's? The PSU's physical size may be slightly different but the connectors are always the standard PSU ones.

This topic has been moved from the section Opinions and Experiences to section Systems by Buwish

It depends... If the mobo circuitry was not designed to supply the power required of a newer graphics card it could definitely burn out the circuit or components.

He's right. I had an HP pc that had a weird psu that used 2 4 pin connectors to power the MB, making it practically impossible to use another power supply.

Really, some odd information above.

I've upgraded four late model HPs in the last year.

(1) HP supports upgrading. They have a great MB doc page and list supported processors and PSU wattage.
(2) The desktops use standard ATX power supplies. The 'slimline' is the exception. You don't have a slimline because they do not come with 300 watt PSUs.
(3) The MBs support standard PCIe x16 slots with decent length clearance
(4) The cases have OK ventilation

Post your HP model number. You can do much better than an HD5450 with a 300 watt PSU. (e.g. HD5770 / HD6770 will work if not overclocked). Or you can upgrade your PSU and go for something stronger.

You are joking, right ?

The PCIe bus has a standard that requires any MB supporting PCIe to supply 75 watts through the socket. And any card that supports PCIe can't draw more than 75 watts through the socket.

Both the HP motherboards and the video cards are PCIe compliant.

"Power

PCI Express cards are allowed a maximum power consumption of 25W (×1: 10W for power-up). Low profile cards are limited to 10W (×16 to 25W). PCI Express Graphics (PEG) cards may increase power (from slot) to 75W after configuration (3.3V/3A + 12V/5.5A).[7] Optional connectors add 75W (6-pin) or 150W (8-pin) power for up to 300W total." http://en.wikipedia.org/wiki/PCIE

You maybe got this confused with the problems DELL had ?

"Issues with Dell power supplies

Older Dell computers, particularly those from the Pentium II and III lines, are notable for using proprietary power wiring on their power supplies and motherboards. While the motherboard connectors appear to be standard ATX, and will actually fit a standard power supply, they are not compatible. Not only have wires been switched from one location to another, but the number of wires for a given voltage have been changed. Thus, the pins cannot simply be rearranged.[2]

The change affects not only 20-pin ATX connectors, but also auxiliary 6-pin connectors. Modern Dell systems might use standard ATX connectors.[3] Dell PC owners should be careful when attempting to change Dell motherboards and power supplies from the original setup, as it can cause damage to the power supply or other components. "

http://en.wikipedia.org/wiki/ATX_motherboard