Ok thanks for the responseSounds like a bug in the Upgrade system somewhere...I just tried to do a PSU upgrade for my system to try and replicate it and it wouldn't let me proceed without also selecting a storage hard drive but nothing about the cooling/fans etc. I'd give them a ring tomorrow/send them a message.
I am trying to purchase a new power supply for my computer through the upgrade feature and it won't let me purchase it and keeps giving this error. The only thing I have added is the PSU and the delivery nothing else.