After looking into this a bit more (because of this thread:
psu) and comparing the specs for the PSUs on
www.antec-inc.com and
www.cwt.com.tw I'm now 99% confident that Antec PSUs are in fact re-badged CWT PSUs (as has been mentioned before).
Basically all the CWT PSUs that Scan are selling - apart from the 550W - seem to match the Antec Smart Power PSUs exactly. The 550W though seems to match the Antec TruPower 550 (as there's no B series 550W CWT PSU listed on the CWT website).
So I reckon:
Antec TruPower = CWT 'A' series PSU
Antec Smart Power = CWT 'B' series PSU
The main difference between the TruPower / A series and the Smart Power / B series is that the B series has a combined rail for 3.3V and 5V whereas the A series has separate rails for all three.
Prices taken from eBuyer and Scan to give a quick comparison (inc VAT but excl delivery):
450W CWT = £34.65, 450W Antec Smart Power = £61.55
550W CWT = £59.93, 550W Antec TruPower = £98.39
For what it's worth apart from comparing specs this is based upon the fact that I recently upgraded from a 380W TruPower to a 450W CWT PSU and the external appearance of both PSUs was indentical and the internal appearance similar.
Anyway - believe it if you want to or don't if you don't but I reckon it's worth a go - esp. for the 450W model which is basically cheap as chips for a decent 450W PSU.