Unless the specifications have changed from when I reviewed the two in 2008 (Trend As. Pro, JSP PowerCap IP) The big difference between the two was the filtration levels, the Trend unit filtration being to En12941:1999 TH 2 P (better) and the Power Cap being to En12941:1998 TH 1 P (SL).
Vital statistics: (2008)
PowerCap IP 570 gram
Battery pack 310 gram (8hr) charge OFF helmet (or still connected)*
Filters* En12941:1998 TH 1 P (SL) (£14)
Eye impact EN166:1995 1 3 B (repl. visor ~£23)
Humidity up to 75%
Noise not quoted but appears comparable with Trend
* Guide notes say no more than 16hrs charge for 8hr bat. Charger is intelligent unit with LED
indication when fully charged.
Trend Airshield pro. 920 gram (1115 gram total in use)
Battery pack 195 gram (8hr) charge in helmet, additional charging dock available.#
Filters* En12941:1999 TH 2 P (£20)
Eye impact EN166:2002 1 3 B (repl. O/lays ~£17.50 (10))
Humidity up to 95%
Noise 70db.
# Guide notes say 14 hrs charge for 8 hr battery, no indication of charge state.
Caution is needed when talking about Power Cap models, only the IP version has significant impact protection.